Musnad Abu Ya'la al-Mawsili 42:289

Zuhayr narrated to us, Yazid bin Harun narrated to us, Muhammad bin Ishaq narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, and from Ubayd Allah bin al-Mughirah bin Mu'ayqib, from 'Amr bin Sulaym, from Abu Sa'id al-Khudri, both of whom said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "O Allah, I take with You a covenant that You will fulfill for me on the Day of Resurrection: You do not break the promise. I am only a human being, so whichever of the Muslims I have harmed, or insulted—or he said: struck, or insulted—then make it for him a prayer, and make it for him a purification and a means of nearness by which You bring him near to You on the Day of Resurrection."