Musnad Ahmad 2:178

Waki’ narrated to us, from Ibn Abi Khalid, from Qays, who said: I saw ‘Umar, and in his hand was a palm branch, and he was seating the people, saying: "Listen to the words of the Caliph of the Messenger of Allah, may Allah bless him and grant him peace." 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: And I saw ‘Umar after that upon the pulpit.