Sayyiduna Jabir (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "(Damage) done by an animal is not compensated; (dying by falling into) a well is not compensated; (dying in) a mine is not compensated; and on buried treasure one fifth is due." Imam al-Sha'bi says: "Rikaz" means ancient treasure (that is, buried treasure).
Ahmad, al-Bazzar and al-Tabarani in al-Mu'jam al-Awsat recorded it; its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الزكاة / 4411