Musnad Ahmad 5:308

'Abdullah narrated to us, Muhammad ibn Sulayman Lawin narrated to me, Hammad ibn Zayd narrated to us, from 'Asim, from Zirr, from Abu Juhayfah, who said: 'Ali addressed us and said: "Shall I not inform you of the best of this nation after its Prophet? Abu Bakr al-Siddiq." Then he said: "Shall I not inform you of the best of this nation after its Prophet and after Abu Bakr?" Then he said: "'Umar."