It is narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The wound caused by an animal carries no liability; if someone dies while extracting from a mine, his blood carries no liability; one who dies in a well also carries no liability; and in buried treasure (rikaz) is one fifth."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16394