Here's a hadith encouraging us to be mindful of our speech. We really should be careful with what we say.

حَدَّثَنِي عَبْدُ اللَّهِ بْنُ مُنِيرٍ، سَمِعَ أَبَا النَّضْرِ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ عَبْدِ اللَّهِ ـ يَعْنِي ابْنَ دِينَارٍ ـ عَنْ أَبِيهِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏

‏ إِنَّ الْعَبْدَ لَيَتَكَلَّمُ بِالْكَلِمَةِ مِنْ رِضْوَانِ اللَّهِ لاَ يُلْقِي لَهَا بَالاً، يَرْفَعُ اللَّهُ بِهَا دَرَجَاتٍ، وَإِنَّ الْعَبْدَ لَيَتَكَلَّمُ بِالْكَلِمَةِ مِنْ سَخَطِ اللَّهِ لاَ يُلْقِي لَهَا بَالاً يَهْوِي بِهَا فِي جَهَنَّمَ ‏"

‏‏‏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."

Sahih al-Bukhari 6478 In-book : Book 81, Hadith 67