Sahih Bukhari Volume 001, Book 003, Hadith Number 091.
Narated By Zaid bin Khalid Al-Juhani : A man asked the Prophet about the picking up of a "Luqata" (fallen lost thing). The Prophet replied, "Recognize and remember its tying material and its container, and make public announcement (about it) for one year, then utilize it but give it to its owner if he comes." Then the person asked about the lost camel. On that, the Prophet got angry and his cheeks or his Face became red and he said, "You have no concern with it as it has its water container, and its feet and it will reach water, and eat (the leaves) of trees till its owner finds it." The man then asked about the lost sheep. The Prophet replied, "It is either for you, for your brother (another person) or for the wolf."