Narrated by Zaid bin Khalid Al-Juhani: A bedouin went to the Prophet (´À║) and asked him about picking up a lost thing. The Prophet (´À║) said, "Make public announcement about it for one year. Remember the description of its container and the string with which it is tied; and if somebody comes and claims it and describes it correctly, (give it to him); otherwise, utilize it." He said, "O Allah's Messenger (´À║)! What about a lost sheep?" The Prophet (´À║) said, "It is for you, for your brother (i.e. its owner), or for the wolf." He further asked, "What about a lost camel?" On that the face of the Prophet (´À║) became red (with anger) and said, "You have nothing to do with it, as it has its feet, its water reserve and can reach places of water and drink, and eat trees."
Source: Sahih Bukhari, 2427