Musnad Abu Ya'la al-Mawsili 152:20

Abu Hisham al-Rifa'i narrated to us, Abu Bakr ibn 'Ayyash narrated to us, al-Hasan ibn 'Amr al-Fuqaymi narrated to us, from Muhammad ibn 'Abd al-Rahman, from his father, from 'Abdullah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The believer is not one who attacks (others' honor), nor one who curses, nor one who is foul-mouthed, nor one who is obscene."