Maliks Muwatta Book 36, Hadith Number 46.
Section : The Judgement on Lost Property.
Malik related to me from Rabia ibn Abi Abd ar-Rahman from Yazid, the mawla of al-Munbaith that Zayd ibn Khalid al-Juhani said, “A man came to the Messenger of Allah, may Allah bless him and grant him peace, and asked him about finds. He said, ‘Memorize the characteristics of the object found, then publicise it for a year. If the owner comes, give it to him. If not, then it is your business.’ He said, ‘What about lost sheep, Messenger of Allah?’ He said, ‘They are yours, your brother’s or the wolf’s.’ He said, ‘And the lost camel?’ He said, ‘It’s none of your concern. It has its water and its feet. It will reach water and eat trees until its owner finds it.'”