Musnad Ahmad 1013:13

Anas ibn Iyad narrated to us, Abu Hazim narrated to me—I do not know it except from Sahl ibn Sa’d—who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Beware of the trivial sins, for the likeness of trivial sins is like a people who camped in the bottom of a valley. This one brought a stick, and that one brought a stick, until they cooked their bread. Indeed, trivial sins, when their perpetrator is taken to account for them, will destroy him."