The Messenger of Allah ﷺ said, "A servant may utter a word without realizing what it contains, and by it he plunges into the Fire a distance greater than that between the east and the west."
أن رسول الله ﷺ قال: إن العبد ليتكلم بالكلمة ما يتبين ما فيها، يهوي بها في النار أبعد ما بين المشرق والمغرب.
Bukhari narrated it in the Book of Softening of Hearts (6477), and Muslim in the Book of Asceticism and Softening of Hearts (298:2988), both of them through Yazid bin Had, from Muhammad bin Ibrahim, from Isa bin Talha, from Abu Hurairah, who mentioned it. The wording given is that of Muslim, and Bukhari's wording is similar.