Musnad Ahmad 30:3305

Ibn Numayr narrated to us, Al-A’mash informed us, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I am only a human being. So, whichever Muslim I have insulted, or cursed, or whipped, make it for him a purification and a mercy."