Musnad Ahmad 456:32

'Abd al-Rahman narrated to us, from Sufyan, from Rabi'ah ibn Abi 'Abd al-Rahman, who said: Yazid, the freed slave of al-Munba'ith, narrated to me, from Zayd ibn Khalid al-Juhani, who said: A Bedouin came to the Prophet, peace and blessings of Allah be upon him, with a lost item. He said: "Announce it for a year, and know its container and its string. If someone comes and informs you about it [give it to him], otherwise, spend it." He said: "O Messenger of Allah, what about a stray sheep?" He said: "It is for you, or for your brother, or for the wolf." He said: "O Messenger of Allah, what about a stray camel?" The face of the Messenger of Allah, peace and blessings of Allah be upon him, changed, and he said: "What do you have to do with it? It has its shoes and its water-skin; it reaches the water and eats the trees."