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 the hadiths whose agreement or disagreement cannot be established, according to instructions received from 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 Quran. 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 Quran.
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 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 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 whinot absolutely established but which is generally considered as reliable is utilized only in the elaboration of the injunctions of the Shari’ah.
The Principles of Interpretation of the Quran
