Sayyiduna al-Jarud (may Allah be pleased with him) said: the Messenger of Allah (peace and blessings be upon him) said: "The lost property of a Muslim is a burning of the Fire, so do not go near it." And he said: "A lost or dropped item that you find, announce it; do not conceal it and do not hide it away. If you recognise the owner, give it to him; otherwise it is the wealth of Allah, who gives it to whomever He wills."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2108