Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with them both) narrates from the Prophet (peace and blessings be upon him) that he was asked about a found item, and he (peace and blessings be upon him) said: "Whatever is found on a frequented road or in an inhabited town, announce it for a year. If its owner comes, give it to him; if he does not come, it is yours. And whatever is found in a ruin, then in it and in buried treasure (rikaz) there is one fifth (khumus)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللقطة / 12058