Sahih al-Bukhari Vol. 8, Book of Good Manners, Hadith 157
Narrated Malik:
Similarly as above (156) adding, "Who believes in Allah and the Last Day should talk what is good or keep quiet." (i.e. abstain from dirty and evil talk, and should think before uttering).
Classification
Sahih (Authentic)
References
Sahih al-Bukhari Vol. 8, Book of Good Manners, Hadith 157