Musnad Abu Ya'la al-Mawsili 110:267

Zuhayr narrated to us, Abu Mus'ab narrated to us, al-Awza'i narrated to us, from al-Zuhri, from Ubayd Allah ibn Abd Allah, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) passed by a dead sheep that its owners had cast away. He said: "By the One in Whose hand is my soul, the world is more insignificant to Allah than this is to its owners."