Musnad Abu Ya'la al-Mawsili 1:80

Zuhayr ibn Harb narrated to us, Uthman ibn Umar narrated to us, Shu'bah narrated to us, Tawbah al-Anbari informed me, he said: I heard Abu al-Siwar Abdullah narrating from Abu Barzah that a man insulted Abu Bakr. He said: So I said, "Shall I strike his neck, O Caliph of the Messenger of Allah?" He said: "No, that is not for anyone after the Messenger of Allah, may Allah bless him and grant him peace."