Musnad Ahmad 33:1009

Hajjaj narrated to us, Ibn Jurayj said: Abu al-Zubayr informed me that he heard Jabir ibn Abdullah saying: I heard the Prophet, peace and blessings of Allah be upon him, saying: "I am only a human being, and I have stipulated to my Lord, the Mighty and Majestic, that any servant among the Muslims whom I have cursed or insulted, that it shall be for him a purification and a reward."