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." (Using translation from Bukhārī 6478)
عَنِ النَّبِيِّ ﷺ قَالَ إِنَّ الْعَبْدَ لَيَتَكَلَّمُ بِالْكَلِمَةِ مِنْ رِضْوَانِ اللهِ لَا يُلْقِي لَهَا بَالًا يَرْفَعُ اللهُ بِهَا لَهُ دَرَجَاتٍ وَإِنَّ الْعَبْدَ لَيَتَكَلَّمُ بِالْكَلِمَةِ مِنْ سَخَطِ اللهِ لَا يُلْقِي لَهَا بَالًا يَهْوِي بِهَا فِي جَهَنَّمَ