It is narrated from Sayyiduna Iyad bin Himar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever finds a luqatah (found property) should take an upright person as witness, then he should not conceal it or hide it, and he should keep announcing it for a year. If its owner comes, well and good; otherwise it is the wealth of Allah, which He gives to whomever He wills."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15060