To make the Heart Tender (Ar-Riqaq)

Bukhari :: Book 8 :: Volume 76 :: Hadith 485

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."