Musannaf Ibn Abi Shayba 36:523

Waki’ narrated to us, from Isma’il, from Qays ibn Abi Hazim, who said: I saw ‘Umar ibn al-Khattab, and in his hand was a palm branch, and he was seating the people and saying: "Listen to the words of the Caliph of the Messenger of Allah." He said: Then a freed slave of Abu Bakr, who was called Shadid, came with a scroll and read it to the people. He said: "Abu Bakr says: 'Listen and obey the one who is in this scroll, for by Allah, I have not been negligent toward you.'" Qays said: Then I saw ‘Umar ibn al-Khattab after that upon the pulpit.