Musnad Ahmad 30:3273

Hajjaj narrated to us, he said: Layth narrated to us, he said: Sa'id ibn Abi Sa'id narrated to us, from Salim, the freed slave of the Nasriyyin, who said: I heard Abu Hurayrah saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "O Allah, Muhammad is only a human being; he gets angry as human beings get angry. And I have taken a covenant with You which You will not break: any believer whom I have harmed, or insulted, or whipped, then make it an expiation for him, and a means of drawing him closer to You on the Day of Resurrection."