Abu Hurairah (May Allah be pleased with him) reported:
I heard the Prophet (ﷺ) saying, "A person utters a word thoughtlessly (i.e., without thinking about its being good or not) and, as a result of this, he will fall down into the fire of Hell deeper than the distance between the east and the west."[Al-Bukhari and Muslim]. (FR)
App reference (FR): Book 18, Hadith 4 (FR)
Arabic/English book reference (FR): Book 18, Hadith 1514 (FR)