Maliks Muwatta Book 56, Hadith Number 6.

Malik related to me from Abdullah ibn Dinar that Abu Salih as-Samman informed him that Abu Hurayra said, “Truly a man utters words to which he attaches no importance, and by them he falls into the fire of Jahannam, and truly a man utters words to which he attaches no importance, and by them Allah raises him into the Garden.”