Sahih Bukhari Volume 3, Book 42, Hadith Number 611.

Narated By Zaid bin Khalid : A man came and asked Allah’s Apostle about picking a lost thing. The Prophet said, “Remember the description of its container and the string it is tied with, and make public announcement about it for one year. If the owner shows up, give it to him; otherwise, do whatever you like with it.” He then asked, “What about a lost sheep?” The Prophet said, “It is for you, for your brother (i.e. its owner), or for the wolf.” He further asked, “What about a lost camel?” The Prophet said, “It is none of your concern. It has its water-container (reservoir) and its feet, and it will reach water and drink it and eat the trees till its owner finds it.”