The principle that the hadith possesses validity, as attested by the Qur'an, is not at all disputed among Shi'ites or in fact among all Muslims. But because of the failure of some of the early rulers of Islam in preserving and guarding the hadith, and the excesses of a group among the companions and followers of the Prophet in propagating hadith literature, the corpus of hadith came to face a certain number of difficulties.
On the one hand, the caliphs of the time prevented the writing down and recording of the hadith and ordered any pages containing texts of hadith to be burned. Sometimes also any increase in activity in the transmission and study of hadith was forbidden. In this way a certain number of hadith were forgotten or lost and a few were even transmitted with a different or distorted meaning.
On the other hand, another tendency also prevailed among another group of the companions of the Holy Prophet who had had the honor of seeing his presence and actually hearing his words. This group, which was respected by the caliphs and the Muslim community, began an intense effort to propagate the hadith.
This was carried to such an extent that sometimes hadith overruled the Qur'an and the injunction of a Qur'anic verse was even considered abrogated by some people through a hadith. Often the transmitters of hadith would travel many miles and hear all the difficulties of travelling in order to hear a single saying.
A group of outsiders who had worn the dress of Islam and also some of the enemies within the ranks of Islam began to change and distort some of the hadith and thus diminished the reliability and validity of the hadith that was then heard and known. For this very reason Islamic scholars began to think of a solution. They created the sciences concerned with the biography of learned men and chains of transmission of hadith in order to be able to discriminate between true and false hadith.
Shi'ism, in addition to seeking to authenticate the chain of transmission of hadith, considers the correlation of the text of the hadith with the Qur'an as a necessary condition for its validity. In Shi'ite sources there are many hadith of the Prophet and the Imams with authentic chains of transmission which themselves assert that a hadith contrary to the Qur'an has no value. Only that hadith can be considered valid which is in agreement with the Qur'an.
Basing itself on these hadiths, Shi'ism does not act upon those hadiths which are contrary to the text of the Qur'an. As for hadiths whose agreement or disagreement cannot be established according to instructions received from the Imams they are passed by in silence without being accepted or rejected.
Needless to say there are also within Shi'ism those who, like a group among the Sunnis act on any hadith whatsoever which they happen to find in different traditional sources.
A hadith heard directly from the mouth of the Prophet or one of the Imams is accepted as is the Qur'an. As for hadiths received through intermediaries, the majority of Shi'ites act upon them if their chain of transmission is established at every step or if there exists definite proof concerning their truth, and, if they are concerned with principles of doctrine which require knowledge and certainty, according to the text of the Qur'an. Other than these two kinds of hadith, no other hadith has any validity concerning principles of doctrine, the invalid hadith being called “tradition with a sincere transmitter” (khabar wahid).
However, in establish in the injunctions of the Shari'ah, because of reasons that have been given, Shi'ites act also on a tradition which is generally accepted as reliable. Therefore, it can be said that for Shi'ism a certain and definitely established hadith is absolutely binding and must be followed, while a hadith which is not absolutely established but which is generally considered as reliable is utilized only in the elaboration of the in junctions of the Shari'ah.
The Islamic sciences, which owe their existence to the ulama of Islam who organized and formulated them, are divided into the two categories of intellectual ('aqli) and transmitted (naqli). The intellectual sciences include such sciences as philosophy and mathematics. The transmitted sciences are those which depend upon transmission from some source, such as the sciences of language, hadith, or history. Without doubt the major cause for the appearance of the transmitted sciences in Islam is the Holy Qur'an. With the exception of a few disciplines such as history, genealogy, and prosody the other transmitted sciences have all come into being under the influence of the Holy Book.
Guided by religious discussions and research, Muslims began to cultivate these sciences, of which the most important are Arabic literature (grammar, rhetoric, and the science of metaphors) and the sciences pertaining to the external form of religion (recitation of the Qur'an, Qur'anic commentary (tafsir) hadith, biography of learned men, the chain of transmission of hadith, and the principles of jurisprudence).
Shi'ites played an essential role in the foundation and establishment of these sciences. In fact, the founders and creators of many of these sciences were Shi'ites. Arabic grammar was put into a systematic form by Abu'l-Aswad al-Du'ali, one of the companions of the Holy Prophet and by Imam Ali. Imam Ali dictated an outline for the organization of the science of Arabic grammar. One of the founders of the science of eloquence (rhetoric and the science o metaphors) was Sahib ibn 'Ahbad a Shi'ite, who was a vizier of the Buyids.
The first Arabic dictionary is the Kitab al-Ayn composed by the famous scholar, Khalil ibn Ahmad al-Basre the Shi'ite who founded the science of prosody. He was also the teacher of the great master of grammar, Sibuwayh.
The Qur'anic recitation of Asim goes back to Ali through one intermediary, and 'Abdallah ibn 'Abbas, who in hadith was the foremost among the companions, was a student of Imam Ali. The contributions of the Household of the Prophet and their associates in hadith and jurisprudence are well known. The founders of the four Sunni schools of law are known to have associated with the fifth and sixth Shi'ite Imams.
In the principles of jurisprudence the remarkable advances accomplished by the Shi'ite scholar Wahid Bihbahani and followed by Shaykh Murtada Ansari have never been matched in Sunni jurisprudence according to existing evidence.