Ḥadīth (Arabic: حديث) which is also called "riwaya" (Arabic: روایة; lit.: narration) is a word in Islamic terminology and religious sciences which refers to sayings quoted from the Prophet (s) and Imams (a) and their conduct.Beside the Qur'an, hadith also has had a central role in Muslims' understanding of religion during history of Islam.
Due to its importance, different sciences have been established to study hadiths from different aspects of reference, content, etc. under the general title of hadith sciences. Issues about the sources of the hadiths are studied in riwayat al-hadith and their content is studied in dirayat al-hadith. rijal and mustalah al-hadith are two branches of riwayat al-hadith. Different branches have been established under the mentioned disciplines to more specifically analyze and check authenticity of hadiths.Among the many hadith books, ten books are more important. Four of them are written by Shi'a and other six ones are written by Sunnis. The four most important Shi'a books are al-Kulayni's al-Kafi, al-Shaykh al-Tusi's Tahdhib al-ahkam and al-Istibsar fi ma ikhtalaf min al-akhbar and al-Shaykh al-Saduq's Man la yahduruh al-faqih. These books are called al-Usul al-'Arba'a or al-Kutub al-'Arba'a (The Four Books).To Sunnis, most authentic books are Sahih al-Bukhari, Sahih Muslim (which are called Sahihayn), Sunan Abi Davud, Sunan al-Tirmidhi, Sunan al-Nasa'i and Sunan Ibn Maja. These books are called al-Sihhah al-Sitta.

123

Meaning

The word "hadith" is an adjective derived from the root ha da tha' (Arabic: ح د ث) meaning "new, story, and narration". Hadith and riwaya are generally different but are used synonymously in most cases in hadith terminology; however, sometimes they are used differently where, Imams' sayings are called hadith and narrations of any topic from other than Imams (a) are called riwaya.Apparently the reason for hadith as khabar is that it is used beside the Qur'an (both of which explain rulings); since, most Sunnis believe that the Qur'an is ancient and thus call the rulings the Prophet (s) issued hadith.From the aspect of content, hadith is divine and from literal aspect, it is humane.

Relation of Hadith with Athar, Khabar and 'Ilm
In recent centuries, three concepts of athar, khabar and 'ilm are in close relation to hadith:

Athar
From literal aspect, Athar means "remains and trace". Among Sunnites, this word refers to any trace remains from religion or religious teachings, whether quoted form the Prophet (s) or quoted through the Followers from the Sahaba about the Prophet's (s) conduct in Medina. However from Shi'a viewpoint, this term is used similar to the meaning of riwaya from Imams (a); and some have associated it with what is quoted from the Companions.

Khabar
There are different opinions about the definition of khabar. Some scholars categorize hadith to Hadith al-Marfu' and called it khabar and Hadith al-Mawquf and called it athar. Some scholars have considered hadith, a saying quoted from Imams (a), khabar as any general quotation from the past and athar even more general than the other two.Some scholars have regarded the three the same to free from disagreements.

'Ilm
This word is no longer used as a term; however, there are many cases of its usage in the first century and some cases in the second century which show that for what today we call hadith, the first word came to one's mind at that time has been 'Ilm.There are certain quotations from the Companions and the Followers in which they expressed their worries about "abandoning of 'ilm" or "'ilm being worn out" and "abandoning of 'ilm" was considered as abandoning of the bearers of 'ilm.

Classification
In hadith studies, there are different classifications of hadith in order to better understand their sources or their content:

-Classification based on the number of the narrators of the source: khabar al-wahid, khabar al-mustafid, and khabar al-mutawatir,
-Classification based on the authenticity of the source: sahih and its subtypes (sahih mudaf, al-muttafaq 'alayh, a'la, awsat, adna), hasan, mawthuq, qawi, da'if and its subtypes (al-mudraj, al-mushtarak, al-musahhaf, al-mu'talaf, and al-mukhtalaf),
-Classification based on connection or disconnection of the chain of references: al-musnad, al-muttasil, al-marfu', al-mawquf, al-maqtu', al-mursal, al-munqati', al-mu'dal or al-mushkil, al-mudmar, al-mu'allaq, al-mu'an'an, al-muhmal,
-Classification based on text: al-nass, al-zahir, al-mu'awwal, al-mutlaq and al-muqayyad, al-'am and al-khass, al-mujmal and al-mubayyan, al-mukatab and al-mukatiba, al-mashhur, al-matruk, al-matruh, al-Hadith al-Qudsi, al-shadh, al-maqlub, al-mutashabih
-Classification based on acting upon the hadith: hujjat and la hujjat, maqbul, nasikh and mansukh

History
In the time of the Prophet (s), 'Ali (a) and some Companions wrote hadiths of the Prophet (s). After the Prophet (s) passed away, writing hadiths among Sunnis became different from among Shi'a. From the first Caliph until 'Umar b. 'Abd al-'Aziz the official policy of the government was opposing narrating and recording hadiths of the Prophet (s) so that they burned many hadith collections.'Umar b. 'Abd al-'Aziz changed the official policy of the government and publishing hadith collections began and al-Sihah al-Sitta were written at the end of third/ninth century, but a century of ban on hadith severely affected the authenticity of later sources.Since the time of Prophet (s) and after him, at the time of the Infallible Imams (a) until the Minor Occultation period Shi'a used to write and compile hadiths. Kitab 'Ali, Jami'a, etc. and Usul arba' mi'a from the companions of Imams (a) were products of that period. In later centuries, collecting and compiling hadiths were done. al-Kutub al-Arba'a were written by collecting the previous hadith sources before the early 5th/11th century.

In Middle and Recent Centuries
Hadith Forgery
As soon as hadith became a source for understanding religion in the first/seventh and second/eighth centuries, abusing it began and some people began forging hadith. The history of forging hadith (wad') and falsely quoting from the Prophet (s) and Imams (a) dates back to the origin of hadith. Hadith scholars benefited from the two sciences of rijal and diraya as the solution for the mentioned problems and though such sciences they could recognize real and fake hadiths.

Studying Source and Content
Criticisms from outside the environment of hadith scholars, made some concerns among them to try to begin professional criticism about hadith themselves. Feeling such a need was not made only from the outside and even existence of some problems such as paradox between different reports made them take the mentioned approach. In such criticisms, even though the general look towards hadith was positive and trustful, but the efforts were towards finding their problems and ways through which readers could remain safe from their harms. The feeling of the need for criticizing hadiths in general made a criticizing system during several centuries which have been studied only in details and a general picture of it has not been studied; a general picture which will be tried to be made below.

Understanding
In order to understand hadith, different issues need to be discussed such as conveying through meaning, language of hadiths, knowing the audience, abrogating and abrogated, different semantic levels of hadiths, interpretation and other topics usually studied in Diraya.

Influence in Islamic Culture and Civilization
Using hadith-derived ideas in the literature of Islamic nations is a phenomenon which has a history as long as the history of the Islamic literature. In addition to usage of hadith-derived ideas in Arabic prose and poetry, examples of using them can be seen in Islamic Iranian literature since its development.

Purification
Distrusting the hadith heritage of Shi'a and the need to return to the Qur'an to access original teachings of Islam draw another group of contemporary scholars towards a kind of purification of the Qur'an and rejecting distortions and deviations. This group were so close to take the approach of Sayyid Qutb in interpreting the Qur'an by the Qur'an and benefiting Qur'anic thoughts for solving social problems; however, criticisms about hadith are usually cautious and relative.A different aspect of purification in Twelver Shi'a seminaries is presented in critical works of Muhammad Taqi Shushtari discussing hadiths and reviewing what he called Ahadith Dakhil meaning "unauthentic hadiths". He also had criticisms about authenticity or recording some words and expressions in Nahj al-balagha. Regarding the authenticity of Nahj al-balagha among Shi'a and criticisms made by Sunnites at that time, such a critical approach was very risky. Regarding the price which had to be paid for such criticisms and their organization in the works of Shushtari, they were the product of a movement of purification and could not be only the result of scholarly and curious efforts.

Orientalists
Also, among orientalists, there was a pessimistic look towards hadith. Until the end of 19th century, orientalists were distrustful both about the sources and validity of text; however, Ignác (Yitzhaq Yehuda) Goldziher (1850 – 1921) made a comprehensive and direct study about hadith and presented a somehow integrated approach about it, which was later completed by others such as Joseph Schacht and was the common approach of orientalists until the end of 20th century. In general, it can be said that orientalists' criticisms of hadith as an important part of Islamic tradition on the one hand and emergence of new needs inside the Islamic world for reconstructing religious institutions on the other hand required Muslims' attention towards this part of their religious tradition and made the positive approach replace the negative one.

Revival of Attention to Hadith
This movement was not yet seriously begun, when Ayatollah Burujirdi (d. 1961) called the Twelver Shi'a seminary to study and research about hadith and prepared the ground for compiling the encyclopedia-like collection of Jami' al-ahadith al-Shi'a. That was when Ahmad Muhammad Shakir (d. 1377/1957-8), who was the chief of Ahl al-hadith (the People of Hadith) of Egypt and one of the pioneers of this movement of reviving hadiths in Egypt and himself had studied hadith in the old Sunni tradition, made great efforts for reviewing and correcting and interpreting most important works of the People of Hadith which resulted in publication of tens of books. His al-Kitab wa al-sunna was a declaration, which although had a Salafi Approach, tried to note the significance of hadith beside tradition for acquiring laws and managing society and criticized those who overlooked hadiths.

Usage for Solving Modern Issues
In recent decades, factors including inclination towards using Islamic teachings more in different levels of life including establishing rules, regulating social and family relations and paying more attention to religious principles in different areas of humanities expanded the grounds for drawing Muslims attention towards hadiths. Answering newly issued problems in the modern era such as problems of women, relation between science and religion, globalization, etc. need to be added to above-mentioned grounds. Issuing such discussions made even intellectuals, social activists and scientist movements who previously did not pay attention to hadith interested. However, one must note that their usage of hadiths is usually very selective and they sometimes pay attention to those texts and hadiths which have great problems of authenticity in the eyes of hadiths scholars.