Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: We went out with the Prophet (peace and blessings be upon him) to Khaybar. One of our men went into a ruin to relieve himself. He took a brick to clean himself with, and gold came out from beneath it. He took it, brought it to the Prophet (peace and blessings be upon him) and told him about it. He said: "Weigh it." He weighed it, and it was worth two hundred dirhams. The Prophet (peace and blessings be upon him) said: "This is buried treasure (rikaz), and one fifth is due on it."
Ahmad and al-Bazzar recorded it. Its chain contains Abd al-Rahman bin Zayd bin Aslam, and he has been criticised; Ibn Adi declared him thiqah (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الزكاة / 4410