It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The animal: the injury it causes is of no account; the mine is of no account; the well is of no account; and in buried treasure (rikaz) there is one fifth."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17687