Musnad Ahmad 33:455

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