Musannaf Ibn Abi Shayba 27:292

Abdullah ibn Idris narrated to us, from Abu Malik al-Ashja'i, from Salim, who said: I said to Ibn al-Hanafiyyah, "Was Abu Bakr the first of the people in Islam?" He said, "No." I said, "Then by what did Abu Bakr rise and surpass [others], until no one is mentioned [in this regard] except Abu Bakr?" He said, "He was the best of them in Islam from the time he accepted Islam until he met Allah."