The Holy Quran, which is the principal source of religious thought in Islam, has given full authority to the external meanings of its words for those who give ear to its message. The same external meaning of the Quranic verses has made the sayings of the Prophet complementary to the words of the Quran and has declared them to be authoritative like the Quran. For as the Quran says: "And We have revealed unto thee the Remembrance that thou mayst explain to mankind that which hath been revealed for them" (Quran, XVI, 44). And, "He it is who hath sent among the unlettered ones a messenger of their own, to recite unto them His revelations and to make them grow, and to teach them the scripture and Wisdom" (Quran, LXII, 2). And "And whatsoever the messenger giveth you, take it. And whatsoever he forbiddeth, abstain (from it)" (Quran, LIX,
    And, "Verily in the messenger of Allah ye have a good example" (Quran, XXXIII, 21). It is quite evident that such verses would not have any real meaning if the words and deeds of the Prophet and his silence and approval were not authority for us just as the Quran itself is. Thus the words of the Prophet are authoritative and must be accepted by those who have heard them orally or received them through reliable transmission. Moreover, through such a completely authentic chain of transmission it is known that the Holy Prophet said, "I leave two things of value amidst you in trust which if you hold on to you will never go astray: the Quran and the members of my household. These will never be separated until the Day of Judgment." According to this and other definitely established hadiths the words of the Family and Household of the Prophet form a corpus that is complementary to the Prophetic hadith.The Household of the Prophet in Islam have authority in religious sciences and are inerrant in the explanation of the teachings and injunctions of Islam. Their sayings, received orally or through reliable transmission, are reliable and authoritative. Therefore, it is clear that the traditional source from which the formal and external aspect of religion is derived, which is an authoritative document and which is also the basic source for the religious thought of Islam, consists of two parts: The Book (Quran) and the Sunnah. By the book is meant the external aspect of the verses of the Holy Quran; and by the sunnah, hadith received from the Prophet and his revered Household.

Traditions of the Companions
    In Shi`ism hadiths transmitted through the companions are dealt with according to this principle: if they deal with the words and actions of the Prophet and do not contradict the hadiths of the Household of the Prophet, they are acceptable. If they contain only the views or opinions of the companions themselves and not those of the Prophet, they are not authoritative as sources for religious injunctions. In this respect the ruling of the companions is like the ruling of any other Muslim. In the same way, the companions themselves dealt with other companions in questions of Islamic law as they would with any Muslim, not as someone special.
    The principle that the hadith possesses validity, as attested by the Quran, 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 contaning texts of hadith to be burned. Soemtimes also any increase in activity in the transmission and study of hadith was forbidden. In this way a certain number of hadiths 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 Quran and the injunction of a quranic verse was even considered abrogated by some people through a hadith. Often the transmitters of hadith would travel many miles and bear 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.

The Method of Shi`ism in Authenticating the 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 Quran as a necessary condition forits validity. In Shi`ite sources there are many hadiths of the Prophet and the Imams with authentic chains of transmission which themselves assert that a hadith contrary to the Quran has no value. Only that hadith can be considered valid which is in agreement with the Quran. Basing itself on these hadiths, Shi`ism does not act upon those hadiths which are contrary to the text of the Quran. 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.

The Method of Shi`ism in Following the Hadith
    A hadith heard directly from the mouth of the Prophet or one of the Imams is accepted as is the Quran. As for hadiths received through intermediaries, the majority of Shi`ites act upon them if their chain of transmission is established at evry step or if there exists definite proof concerning their truth, and, if they are cocerned with principles of doctrine which require knowledge and certainty, according to the text of the Quran. Other than these two kinds of hadith, no other hadith has any validity concerning principles of doctrines, the invalid hadith being called "tradition with a single transmitter" (khabar wahid). However, in establishing 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 relaible. 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 injunctions of the Shari`ah.