Musnad Ahmad 5:315

'Abdullah narrated to us, Wahb ibn Baqiyyah al-Wasiti narrated to us, Khalid ibn 'Abdullah informed us, from Bayan, from 'Amir, from Abu Juhayfah, who said: 'Ali ibn Abi Talib said: "Shall I not inform you of the best of this nation after its Prophet? Abu Bakr, then 'Umar, then another man."