Sahih Bukhari
Virtues and Merits of the Prophet (pbuh) and his Companions
Volume: 004 / Book Number: 056 / Hadith Number: 759
Narrated 'Abdullah bin 'Amr:
The Prophet never used bad language neither a "Fahish nor a Mutafahish. He used to say "The best amongst you are those who have the best manners and character." (See Hadith No. 56 (B) Vol. 8)