Sahih Muslim
The Book of Poetry (Kitab Al-Shir)
Book Number: 028 / Hadith Number: 5605
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: The truest word uttered by a poet is this verse of Labid:" Behold! apart from Allah everything is vain," and Umayya b. Abu Salt was almost a Muslim.