Musnad Ahmad 1:2

Waki’ narrated to us, he said: Mis’ar and Sufyan narrated to us, from Uthman ibn al-Mughirah al-Thaqafi, from Ali ibn Rabi’ah al-Walibi, from Asma ibn al-Hakam al-Fazari, from Ali, may Allah be pleased with him, who said: When I heard a hadith from the Messenger of Allah, may Allah bless him and grant him peace, Allah would benefit me with it as He willed. And if someone else narrated it to me from him, I would make him swear an oath, and if he swore to me, I would believe him. Abu Bakr, may Allah be pleased with him, narrated to me—and Abu Bakr spoke the truth—that he heard the Prophet, may Allah bless him and grant him peace, say: "There is no man who commits a sin, then performs ablution and perfects the ablution—Mis’ar said: 'and prays,' and Sufyan said: 'then prays two rak'ahs'—and then seeks the forgiveness of Allah, the Mighty and Majestic, but He will forgive him."