Maliks Muwatta Book 056, Hadith Number 006.

Section : The Order to be Mindful in Speech.

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."