Sahih Muslim 42b

A man asked the Prophet (may Allah's peace and blessings be upon him) about the ruling on lost property, such as gold, silver, camels, and sheep. The Prophet (may Allah's peace and blessings be upon him) clarified to him the ruling on these things so that it could be an example of other similar lost properties that would, thus, take the same ruling. He said about gold and silver: Remember the description of its container and the string with which it is tied, so that you can distinguish it from your own property and you can tell if it belongs to those who claim it.

If one comes claiming it, and his description of such an item matches the description that you know, then give it to that person; otherwise, it will be clear to you that his claim is false. Then, the Prophet (may Allah's peace and blessings be upon him) ordered him to announce it for one year after finding it. The announcement should be made in public places where people gather like the markets, at the doors of mosques, in public assembly places, and in the place where it was found.

Then, the Prophet (may Allah's peace and blessings be upon him) allowed him - after announcing it in public for one year and not finding its owner - to spend it or use it. If the owner appears at any time, then the one who found it should give it to him. As for a lost camel and the like, the Prophet (may Allah's peace and blessings be upon him) prohibited him from taking it, because it does not need anyone to protect it.

It is naturally an animal that can take care of itself and protect itself from small wild animals. A camel has hooves and legs that can travel long distances; its neck enables it to eat from the trees and drink water, and its stomach is equipped to store water and food. So the camel can protect itself until it is found by its owner who will be looking for it in the place where it got lost. As for lost sheep and other small animals, the Prophet (may Allah's peace and blessings be upon him) ordered him to take it and protect it from destruction or being attacked by predatory animals.

After taking possession of it, either its owner will come and claim it, or a year will pass after announcing it with no one to claim it, so it will be a property of the one who found it.