Musnad Ahmad 551:13

Hassan narrated to us, he said: Ibn Lahi'ah narrated to us, he said: Yazid ibn Abi Habib narrated to us, he said: Suwayd ibn Qays informed me, from Qays ibn Shafi', that 'Amr ibn al-'As said: I said: "O Messenger of Allah, I pledge allegiance to you on the condition that what has preceded of my sins be forgiven for me." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Islam wipes away what was before it, and indeed, the Hijrah (migration) wipes away what was before it." 'Amr said: By Allah, I was the most bashful of people before the Messenger of Allah (peace and blessings of Allah be upon him). I never filled my eyes with the Messenger of Allah (peace and blessings of Allah be upon him), nor did I speak back to him with what I wanted, until he joined Allah (the Mighty and Majestic) out of bashfulness before him.