Musannaf Ibn Abi Shayba 33:165

Ghundar narrated to us, from Shu'bah, from al-Hakam, who said: I heard Ibn Abi Layla narrating from Abdullah ibn Rabi'ah, who said: The Messenger of Allah (peace be upon him) was on a journey, and he came upon a discarded sheep. He said: "Do you see this as being insignificant to its owners?" They said: "Yes." He said: "The world is more insignificant to Allah than this is to its owners."