حدیث، در اصطلاح مسلمانان به سخنان پیامبران گفته میشود. شیعیان به سخنان اهل بیت نیز حدیث میگویند. در اصطلاح دانشمندان علم حدیث، به کلامی که حاکی از کردار یا تقریر معصوم (محمد، پیامبراسلام) است، «حدیث» و گاه «خبر» یا «روایت» گفته میشود. شیعیان متعقدند: «حدیث، بهدلیل انتساب آن به معصوم و وحیانی بودن محتوای آن، حجت بوده و میتواند مبنای عمل قرار گیرد»
بنابر عقیده مسلمانان، قرآن، به مثابه قانون اساسی اسلام، بیشتر کلیات را بیان کرده و تبیین تفاصیل و جزئیات را به روایات واگذار کرده است، از اینرو روایات، پس از قرآن، مهمترین منبع شناخت دین اسلام به شمار میآید. بدین جهت، مسلمانان به فراگیری، ثبت و تدوین احادیث، بهرغم برخی فراز و نشیبها، توجه کرده و مجموعههای حدیثی را شامل هزاران روایت در تمام موضوعات مورد نیاز دینداران، فراهم آوردند. پس از آن، دانشهای رجال، تاریخ حدیث، مصطلحات حدیث، فقه الحدیث و... برای حفظ، نشر، فهم و تبیین میراث روایی پدید آمد.
تدوین هزاران اثر حدیثی نشان میدهد که مسلمانان، از آغاز تاکنون، پس از قرآن، بیشتر به حدیث توجه کردهاند. در دوران معاصر نیز اندیشمندان مسلمان با نگاهی دوباره به میراث روایی، کوشش گستردهای را برای بهره جستن هر چه بیشتر از این منبع آغاز کردند و با تأسیس دانشگاهها، مراکز تحقیقاتی حدیثی و... در این راه گامهایی برداشتند.
دانشمندان علم اصول فقه، به نقل کردن سنّت، حدیث (خبر) میگویند . 
حدیث، در لغت به معنی هر چیز نو و جدید است، خبر و کلام را نیز حدیث خوانند. ابوالبقاء گوید: «حدیث، اسم مصدر از تحدیث به معنی خبر دادن است، سپس قول یا فعل یا تقریری که به محمد منسوب شود را بدان نامیدهاند، و جمع آن احادیث بر خلاف قیاس است». در اصطلاح، حدیث عبارت است از سخنی که حاکی از قول یا فعل یا تقریر معصوم باشد. چنان که جمعی از علمای درایة و اصول تصریح کردهاند.
در طول سدههای بعد از زندگانی محمد و اهل بیت، احادیث توسط شیعه و سنی در مجموعههایی گردآوری و مدون شده است. در میان مجموعه کتابهای حدیث، صحاح سته درنزد اهل سنت و اصول اربعه نزد شیعه از اهمیت بسزایی برای مسلمانان برخوردار است.
اصطلاح علم حدیث از نظر فقهای اسلامی، علمی است که توسط آن اقوال و افعال و احوال یا تقریر محمد و امامان (از نظر شیعیان) شناخته میشود و چون احادیث رسیده از ایشان، شامل گفتههای آنان هم میشود شامل گفته و نیز نام وسائطی است که کلام مزبور را از وی روایت کردهاند. میتوان گفت که اصطلاح «علم حدیث» یعنی دانستن (علم به) قوانینی که به وسیلهٔ آن احوال سند و متن حدیث شناخته میشود.
تقسیمات علم حدیث[ویرایش]
روایت الحدیث (اصول الحدیث) علمی است که از کیفیت اتصال احادیث به پیامبر اسلام و امام، از جهت احوال روات (که آیا ضابط و عادلند؟) و از لحاظ کیفیت سند (که آیا متصل است یا منقطع؟) و غیر اینها گفتگو میکند و خود شامل دو بخش است:
درایة الحدیث (در مقابل روایة الحدیث) علمی است که از مفاد الفاظ متن حدیث چون شرح لغات حدیث و بیان حال حدیث از لحاظ اطلاق و تقیید و عموم و خصوص و داشتن معارض و مانند اینها بحث میکند که مناسب است نام این قسمت را فقه الحدیث گذارند. بخش اول را اصول الحدیث نیز مینامند.
نوشتار اصلی: قرآنیان
مکتب و شاخهای از مسلمانان است که قرآن را تنها کتاب و مرجع مستند برای ایمان، انجام مناسک و اعمال دینی خود، قبول دارند. اینان حدیث و گاه سنت را که عموم مسلمانان و روحانیان رسمی بعنوان مرجع مورد قبول برای انجام مناسک و ملاک ایمان و اعتقاد میدانند، ملازم و مترادف اعتقاد دینی ندانسته و در رفتار دینی خود الزامی به رعایت آن ندارند. 
Hadith (Arabic: حديث, // or //) in religious use is often translated as 'tradition', meaning a report of the deeds and sayings of Muhammad. The Hadith literature does not qualify as "primary source" material as it was compiled from reports of hearsay that were present in society around the time of their compilation, which was well after the death of the Prophet Muhammad. Bukhari's collection which is considered by many traditional religious scholars as the most reliable was compiled two centuries after the death of the Prophet. Hadiths claims to originate from important characters of the earliest years of Islam such as the companions of Muhammad or Shia Imams/Religious leaders. These hadith narrations have formed the basis of "Islamic law", despite the contradictions they contain with regards to the Quran, for example the punishment for Zina in the hadith (stoning to death) contradicts the Quran and yet it is still the prescribed punishment by the established schools of thought such as the Hanafis. The Hadith has also had a profound influence on molding the commentaries (tafsir) on the Quran. Much of early Islamic history that is widely available is also based on the hadith.
Each hadith is composed of two parts, a chain of authorities reporting the hadith (isnad), which would not stand the tests of "reliability" according to modern standards of historical analysis, and the text itself (matn). Hadiths are regarded by traditional Islamic schools of jurisprudence as important tools for understanding the Quran and in matters of jurisprudence. Hadith were evaluated and gathered into large collections during the 8th and 9th centuries. These works are referred to in matters of Islamic law and history to this day.
Clerics and jurists of all denominations classify individual hadith as sahih (authentic), hasan (good) and da'if (weak). However, different traditions within each denomination, and different scholars within each tradition, may differ as to which hadith should be included in which category.
In Arabic the word ḥadīth (Arabic: حديث ḥadīth IPA: [ħaˈdiːθ]) means a "report, account, or narrative". The Arabic plural is ʾaḥādīth (أحاديث) (IPA: [ʔaħaːˈdiːθ]). Hadith also refers to the speech of a person. It is a noun.
In Islamic terminology, the term hadith refers to reports of statements or actions of Muhammad, or of his tacit approval or criticism of something said or done in his presence. Classical hadith specialist Ibn Hajar al-Asqalani says that the intended meaning of hadith in religious tradition is something attributed to Muhammad but that is not found in the Quran. Other associated words possess similar meanings including: khabar (news, information) often refers to reports about Muhammad, but sometimes refers to traditions about his companions and their successors from the following generation; conversely, athar (trace, vestige) usually refers to traditions about the companions and successors, though sometimes connotes traditions about Muhammad. The word sunnah (custom) is also used in reference to a normative custom of Muhammad or the early Muslim community.
Hadith Qudsi (or Sacred Hadith) is a sub-category of hadith which are sayings of Muhammad. Muslims regard the Hadith Qudsi as the words of God (Arabic: Allah), repeated by Muhammad and recorded on the condition of an isnad. According to as-Sayyid ash-Sharif al-Jurjani, the Hadith Qudsi differ from the Quran in that the former are "expressed in Muhammad's words", whereas the latter are the "direct words of God".
An example of a Hadith Qudsi is the hadith of Abu Hurairah who said that Muhammad said:
The two major aspects of a hadith are the text of the report (the matn), which contains the actual narrative, and the chain of narrators (the isnad), which documents the route by which the report has been transmitted. The sanad, literally 'support', is so named due to the reliance of the hadith specialists upon it in determining the authenticity or weakness of a hadith. The isnad consists of a chronological list of the narrators, each mentioning the one from whom they heard the hadith, until mentioning the originator of the matn along with the matn itself.
The first people to hear hadith were the companions who preserved it and then conveyed it to those after them. Then the generation following them received it, thus conveying it to those after them and so on. So a companion would say, "I heard the Prophet say such and such." The Follower would then say, "I heard a companion say, 'I heard the Prophet.'" The one after him would then say, "I heard someone say, 'I heard a Companion say, 'I heard the Prophet..." and so on.
The overwhelming majority of Muslims consider hadith to be essential supplements to and clarifications of the Quran, Islam's holy book, as well as in clarifying issues pertaining to Islamic jurisprudence. Ibn al-Salah, a hadith specialist, described the relationship between hadith and other aspect of the religion by saying: "It is the science most pervasive in respect to the other sciences in their various branches, in particular to jurisprudence being the most important of them." "The intended meaning of 'other sciences' here are those pertaining to religion," explains Ibn Hajar al-Asqalani, "Quranic exegesis, hadith, and jurisprudence. The science of hadith became the most pervasive due to the need displayed by each of these three sciences. The need hadith has of its science is apparent. As for Quranic exegesis, then the preferred manner of explaining the speech of God is by means of what has been accepted as a statement of Muhammad. The one looking to this is in need of distinguishing the acceptable from the unacceptable. Regarding jurisprudence, then the jurist is in need of citing as an evidence the acceptable to the exception of the later, something only possible utilizing the science of hadith."
Traditions of the life of Muhammad and the early history of Islam were passed down mostly orally for more than a hundred years after Muhammad's death in AD 632. Muslim historians say that Caliph Uthman ibn Affan (the third khalifa (caliph) of the Rashidun Empire, or third successor of Muhammad, who had formerly been Muhammad's secretary), is generally believed to urge Muslims to record the hadith just as Muhammad suggested to some of his followers to write down his words and actions.
Uthman's labours were cut short by his assassination, at the hands of aggrieved soldiers, in 656. No sources survive directly from this period so we are dependent on what later writers tell us about this period.
By the 9th century the number of hadiths had grown exponentially. Islamic scholars of the Abbasid period were faced with a huge corpus of miscellaneous traditions, some of them flatly contradicting each other. Many of these traditions supported differing views on a variety of controversial matters. Scholars had to decide which hadith were to be trusted as authentic and which had been invented for political or theological purposes. To do this, they used a number of techniques which Muslims now call the science of hadith.
Shia and Sunni textual traditions
Sunni and Shia hadith collections differ because scholars from the two traditions differ as to the reliability of the narrators and transmitters. Narrators who took the side of Abu Bakr and Umar rather than Ali, in the disputes over leadership that followed the death of Muhammad, are seen as unreliable by the Shia; narrations sourced to Ali and the family of Muhammad, and to their supporters, are preferred. Sunni scholars put trust in narrators, such as Aisha, whom Shia reject. Differences in hadith collections have contributed to differences in worship practices and shari'a law and have hardened the dividing line between the two traditions.
Extent and nature of the textual corpus in the Sunni tradition
In the Sunni tradition, the number of such texts is ten thousand plus or minus a few thousand. But if, say, ten companions record a text reporting a single incident in the life of the prophet, hadith scholars can count this as ten hadiths. So Musnad Ahmad, for example, has over 30,000 hadiths—but this count includes texts that are repeated in order to record slight variations within the text or within the chains of narrations. Identifying the narrators of the various texts, comparing their narrations of the same texts to identify both the soundest reporting of a text and the reporters who are most sound in their reporting occupied experts of hadith throughout the 2nd century. In the 3rd century of Islam (from 225/840 to about 275/889), hadith experts composed brief works recording a selection of about two- to five-thousand such texts which they felt to have been most soundly documented or most widely referred to in the Muslim scholarly community. The 4th and 5th century saw these six works being commented on quite widely. This auxiliary literature has contributed to making their study the place of departure for any serious study of hadith. In addition, Bukhari and Muslim in particular, claimed that they were collecting only the soundest of sound hadiths. These later scholars tested their claims and agreed to them, so that today, they are considered the most reliable collections of hadith. Toward the end of the 5th century, Ibn al-Qaisarani formally standardized the Sunni canon into six pivotal works, a delineation which remains to this day.
Over the centuries, several different categories of collections came into existence. Some are more general, like the muṣannaf, the muʿjam, and the jāmiʿ, and some more specific, either characterised by the topics treated, like the sunan (restricted to legal-liturgical traditions), or by its composition, like the arbaʿīniyyāt (collections of forty hadiths).
Extent and nature of the textual corpus in the Shia tradition
Shi'a Muslims do not use the six major hadith collections followed by the Sunni, as they do not trust many of the Sunni narrators and transmitters. They have their own extensive hadith literature. The best-known hadith collections are The Four Books, which were compiled by three authors who are known as the 'Three Muhammads'. The Four Books are: Kitab al-Kafi by Muhammad ibn Ya'qub al-Kulayni al-Razi (329 AH), Man la yahduruhu al-Faqih by Muhammad ibn Babuya and Al-Tahdhib and Al-Istibsar both by Shaykh Muhammad Tusi. Shi'a clerics also make use of extensive collections and commentaries by later authors.
Hadith studies are a number of methods of evaluation developed by early Muslim scholars in determining the veracity of reports attributed to Muhammad. This is achieved by analyzing the text of the report, the scale of the report's transmission, the routes through which the report was transmitted, and the individual narrators involved in its transmission. On the basis of these criteria, various classifications were devised for hadith. The earliest comprehensive work in hadith studies was Abu Muhammad al-Ramahurmuzi's al-Muhaddith al-Fasil, while another significant work was al-Hakim al-Naysaburi's Ma‘rifat ‘ulum al-hadith. Ibn al-Salah's ʻUlum al-hadith is considered the standard classical reference on hadith studies.
By means of hadith terminology, hadith are categorized as ṣaḥīḥ (sound, authentic), ḍaʿīf (weak), or mawḍūʿ (fabricated). Other classifications used also include: ḥasan (good), which refers to an otherwise ṣaḥīḥ report suffering from minor deficiency, or a weak report strengthened due to numerous other corroborating reports; and munkar (denounced) which is a report that is rejected due to the presence of an unreliable transmitter contradicting another more reliable narrator. Both sahīh and hasan reports are considered acceptable for usage in Islamic legal discourse. Classifications of hadith may also be based upon the scale of transmission. Reports that pass through many reliable transmitters at each point in the isnad up until their collection and transcription are known as mutawātir. These reports are considered the most authoritative as they pass through so many different routes that collusion between all of the transmitters becomes an impossibility. Reports not meeting this standard are known as aahad, and are of several different types.
Another area of focus in the study of hadith is biographical analysis (‘ilm al-rijāl, lit. "science of people"), in which details about the transmitter are scrutinized. This includes analyzing their date and place of birth; familial connections; teachers and students; religiosity; moral behaviour; literary output; their travels; as well as their date of death. Based upon these criteria, the reliability (thiqāt) of the transmitter is assessed. Also determined is whether the individual was actually able to transmit the report, which is deduced from their contemporaneity and geographical proximity with the other transmitters in the chain. Examples of biographical dictionaries include: Abd al-Ghani al-Maqdisi's Al-Kamal fi Asma' al-Rijal, Ibn Hajar al-Asqalani's Tahdhīb al-Tahdhīb and al-Dhahabi's Tadhkirat al-huffaz.
Criticism of Hadith by Islamic Scholars
Syed Ahmed Khan (1817–1898) is often considered the founder of the modernist movement within Islam, noted for his application of "rational science" to the Quran and Hadith and his conclusion that the Hadith were not legally binding on Muslims. His student, Chiragh ‘Ali, went further, suggesting nearly all the Hadith were fabrications.
Ghulam Ahmed Pervez (1903–1985) was a noted critic of the Hadith and believed that the Quran alone was all that was necessary to discern God's will and our obligations. A fatwa, ruling, signed by more than a thousand orthodox clerics, denounced him as a 'kafir', a non-believer. His seminal work, Maqam-e Hadith argued that the Hadith were composed of "the garbled words of previous centuries", but suggests that he is not against the idea of collected sayings of the Prophet, only that he would consider any hadith that goes against the teachings of Quran to have been falsely attributed to the Prophet.
The 1986 Malaysian book "Hadith: A Re-evaluation" by Kassim Ahmad was met with controversy and some scholars declared him an apostate from Islam for suggesting that "“the hadith are sectarian, anti-science, anti-reason and anti-women".
Western academic scholarship
Early Western exploration of Islam consisted primarily of translation of the Qur'an and a few histories. In the 19th century, scholars translated and commented upon a great variety of Muslim religious texts; by the beginning of the 20th century, Western scholars of Islam started to critically engage with these Islamic texts. Ignaz Goldziher is the best known of these turn-of-the-century critics, who also included D. S. Margoliuth, Henri Lammens, and Leone Caetani. Goldziher writes, in his Mohammedan Studies: "... it is not surprising that, among the hotly debated controversial issues of Islam, whether political or doctrinal, there is not one in which the champions of the various views are unable to cite a number of traditions, all equipped with imposing isnads". John Esposito notes that "Modern Western scholarship has seriously questioned the historicity and authenticity of the hadith", maintaining that "the bulk of traditions attributed to the Prophet Muhammad were actually written much later." He mentions Joseph Schacht as one scholar who argues this, claiming that Schacht "found no evidence of legal traditions before 722," from which Schacht concluded that "the Sunna of the Prophet is not the words and deeds of the Prophet, but apocryphal material" dating from later.
Contemporary Western scholars of hadith include: Herbert Berg, Fred M. Donner and Wilferd Madelung. Madelung has immersed himself in the hadith literature and has made his own selection and evaluation of tradition. Having done this, he is much more willing to trust hadith than many of his contemporaries. Madelung said of hadith: "Work with the narrative sources, both those that have been available to historians for a long time and others which have been published recently, made it plain that their wholesale rejection as late fiction is unjustified and that with [not without] a judicious use of them, a much more reliable and accurate portrait of the period can be drawn than has been realized so far."
Harald Motzki said: "The mere fact that ahadith and asanid were forged must not lead us to conclude that all of them are fictitious or that the genuine and the spurious cannot be distinguished with some degree of certainty."