Musnad Ahmad 5:466

'Abdullah narrated to us, Wahb ibn Baqiyyah narrated to me, Khalid informed us, from 'Ata'—meaning Ibn al-Sa'ib—from 'Abd Khayr, from 'Ali, who said: "Shall I not inform you of the best of this nation after its Prophet, may Allah bless him and grant him peace? Abu Bakr. Then the best of it after Abu Bakr is 'Umar. Then Allah places the good wherever He wills."