Musnad Ahmad 26:398

Aswad narrated to us, Abu Bakr informed us, from al-Hasan ibn ‘Amr, from Muhammad ibn ‘Abd al-Rahman ibn Yazid, from his father, from ‘Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the believer is not one who frequently curses, nor one who frequently defames, nor one who is obscene, nor one who is vulgar."