Musnad Ahmad 32:666

Musa ibn Dawud narrated to us, Fulayh ibn Sulayman narrated to us, from Hilal—meaning ibn Ali—from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) was not one who insulted, nor was he foul-mouthed, nor was he a curser. He would say to one of us when rebuking him: "What is the matter with him? May his forehead be rubbed with dust."