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

English translation · Sahih al-Bukhari