It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The wound caused by an animal is without liability (there is no penalty on the owner), the well is without liability, the mine is without liability, and in rikaz (buried treasure) there is khums."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7647