Musnad Ahmad 32:334

Abu Amir narrated to us, Fulayh narrated to us, from Hilal 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 one who cursed, nor one who used foul language. When he would rebuke one of us, he would say: "What is the matter with him? May his forehead be rubbed with dust."