(23) باب حِفْظِ اللِّسَانِ
Narrated Abu Huraira:
The Prophet; said, "A slave (of Allah) may utter a word which pleases Allah without giving it much importance, and because of that Allah will raise him to degrees (of reward): a slave (of Allah) may utter a word (carelessly) which displeases Allah without thinking of its gravity and because of that he will be thrown into the Hell-Fire."
Reference: Sahih al-Bukhari 6478
In-book reference: Book 81, Hadith 67
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 76, Hadith 485