Sahih Bukhari Volume 001, Book 003, Hadith Number 111.
Narated By Ash-Sha'bi : Abu Juhaifa said, "I asked Ali, 'Have you got any book (which has been revealed to the Prophet apart from the Qur'an)?' 'Ali replied, 'No, except Allah's Book or the power of understanding which has been bestowed (by Allah) upon a Muslim or what is (written) in this sheet of paper (with me).' Abu Juhaifa said, "I asked, 'What is (written) in this sheet of paper?' Ali replied, it deals with The Diyya (compensation (blood money) paid by the killer to the relatives of the victim), the ransom for the releasing of the captives from the hands of the enemies, and the law that no Muslim should be killed in Qisas (equality in punishment) for the killing of (a disbeliever).