Musnad Ahmad 25:1188

Muhammad ibn Mus'ab narrated to us, al-Awza'i narrated to us, from al-Zuhri, from 'Ubayd Allah, from Ibn 'Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) 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."