On page 124 of Al-Manaqib, Al-Khatib al-Khwarizmi al-Hanafi has quoted a letter written by Mu`awiya to `Amr b. al-`As in which he seeks to entice him to help him in the Battle of Siffin. Then he refers to a letter written by `Amr in answer to Mu`awiya. The two letters can be found in the biography of `Amr b. al-`As. In his letter, `Amr states:

“As for your accusing Abu’l Hasan, the brother of the Messenger of Allah and his testamentary trustee (wasi), of oppression and envy of `Uthman, and your calling his companions transgressors and alleging that he incited them to kill him – this is a lie and deviation from the right way. Woe be to you, O Mu`awiya! Do you not know that Abu’l Hasan sacrificed himself for the Messenger of Allah, blessings and salutations of Allah on him, and spent the night on his bed [when the Prophet was migrating in that night from Makka to Madina]? He was the possessor of precedence in Islam and the Hijra; and the Messenger of Allah, blessings and salutations of Allah on him, had said of him:

‘He is from me and I am from him. His station in relation to me is that of Harun’s (Aaron) in relation to Musa (Moses) except that there is no Prophet after me’.

And he said concerning him on the day of Ghadir Khumm:

‘Surely, of whomsoever I am master (mawla), `Ali is his master. O Allah, befriend one who befriends him and be at enmity with one who shows enmity to him, and help one who helps him, and forsake one who forsakes him.’”