Sahih Muslim
The Book Pertaining to Punishments Prescribed by Islam (Kitab Al-Hudud)
Book Number: 017 / Hadith Number: 4239
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: No requital is payable for a wound caused by an animal, for (falling into) a well and a mine, and one-fifth (is the share of the government) in the buried treasure (treasure-trove).