Musnad Ahmad 5:490

Abdullah narrated to us, Abu Salih al-Hakam ibn Musa narrated to us, Shihab ibn Khirash narrated to us, al-Hajjaj ibn Dinar narrated to us, from Husayn ibn Abd al-Rahman, from Abu Juhayfah, who said: I used to think that Ali was the best of people after the Messenger of Allah, may Allah bless him and grant him peace—then he mentioned the hadith—I said: "No, by Allah, O Commander of the Faithful, I did not think that anyone among the Muslims after the Messenger of Allah, may Allah bless him and grant him peace, was better than you." He said: "Shall I not tell you of the best of people who was after the Messenger of Allah, may Allah bless him and grant him peace?" I said: "Yes." He said: "Abu Bakr." Then he said: "Shall I not inform you of the best of people who was after the Messenger of Allah, may Allah bless him and grant him peace, and Abu Bakr?" I said: "Yes." He said: "Umar."