Usul al-Kafi
Book 2: The Book of Excellence of Knowledge

Chapter 21

Traditions 144 to 146
Conflicting traditions

144. Imam Ali (p): There is not a single verse of the Noble Quran that was revealed to Prophet Muhammad (p) and which the Prophet (p) did not recite to me and dictate to me and which I did not write down with my own hands.(B2, C21, T1)

145. 7. Imam Jafar as-Sadiq (p) was asked: What should a person do when he finds two contradictory versions of a tradition, one of them commanding him to do something and the other forbidding him, and both the narrators belonging to his community.
The Imam (p): He should wait till he is able to verify from a reliable person. In such case it is permissible for him to postpone action till he finds out the truth.

146. 10. A believer asked Imam Jafar as-Sadiq (p): Two persons belonging to our people quarrelling about debt or inheritance; refer their dispute to the ruler of the time or the judge appointed by him. Will it be lawful for them to obey?
The Imam (p): Whoever has his dispute settled by the ruler or the judge appointed by him, whether right or wrong, has in fact got his dispute settled by the Taghut*. And the profits out of that decision will be ill-gotten for him, however lawful his ownership may be. The reason is that he has secured the ownership through the Taghut while God has enjoined upon people to reject his verdict. God, the Almighty, the Sublime, said: They intend to resort to the judgment of Taghut though they were commanded to reject him (Q, 4:60). (Taghut is a Quranic term for a being who is strongly rebellious and defiant to God like Nimrod and Pharaoh.)
The Believer: Then what should they do?
The Imam (p): They should refer to one among you who is well versed in our traditions, and has a deep insight into imperatives, prohibitions and divine commands communicated by us. Since I have appointed him as your judge, they must accept him as their arbitrator. If such a person issues a verdict according to our commands and the person concerned does not accept it, then the person has actually made light of the divine commands and has rejected us. And he who rejects us actually rejects God, the Almighty. Such a person has entered the realm of polytheism…