20- In referencing the statements related to the causes of hadith, the narrators of hadith, and history (the books of criticism and praise), I have relied on historical books. I have discussed most of the statements with Muhammad bin Ismail Bukhari, and some statements with Darimi and Abu Zur’ah. I have conversed about most statements with Muhammad bin Ismail Bukhari, and very few statements with Abdullah bin Ahmad and Abu Zur’ah Razi. In the knowledge of the causes of hadith, history, and chains of transmission, I have not found anyone in Iraq and Khorasan greater in knowledge than Muhammad bin Ismail Bukhari.