Bilal bin Harith (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Indeed, a person utters a good word and he does not realize its significance, yet because of it Allah writes His pleasure for him until the Day of Resurrection. And indeed, a person utters a bad word and he does not realize its importance, so because of it Allah writes His displeasure for him until the Day of Resurrection." Sharh al-Sunnah. And Imam Malik, Tirmidhi, and Ibn Majah have narrated a similar report. Its chain is Hasan. Narrated in Sharh al-Sunnah, Malik, Tirmidhi, and Ibn Majah.