Musannaf Ibn Abi Shayba 21:232

Muhammad ibn Bishr narrated to us, Zakariya ibn Abi Za'idah narrated to us, Mansur ibn al-Mu'tamir narrated to us, he said: Rib'i ibn Hirash narrated to us, from Imran ibn Husayn, that he said: Husayn came to the Prophet, may Allah bless him and grant him peace, before he embraced Islam, and said: "O Muhammad, what do you command me to say?" He said: "Say: 'O Allah, I seek refuge in You from the evil of my soul, and I ask You to decree for me the most guided of my affairs.'" He said: Then Husayn embraced Islam afterward, then he came to the Prophet, may Allah bless him and grant him peace, and said: "I had asked you the first time, and I am now saying: what do you command me?" He said: "Say: 'O Allah, forgive me for what I have kept secret and what I have made public, and what I have done by mistake and what I have done intentionally, and what I have been ignorant of and what I have known.'"