Musnad Abu Ya'la al-Mawsili 1:11

'Ali said: I was a man who, 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 much as He willed to benefit me. And if one of his companions narrated to me, I would make him swear an oath, and if he swore to me, I would believe him. Abu Bakr narrated to me—and Abu Bakr spoke the truth—that he heard the Messenger of Allah (may Allah bless him and grant him peace) say: "Any servant who commits a sin, then performs ablution and perfects the ablution, then stands and prays, then asks Allah for forgiveness, except that He forgives him." Then he recited: "And those who, when they commit an immorality or wrong themselves [thereby]..." (Al-Imran: 135).