Sahih Bukhari
Blood Money (Ad-Diyat)
Volume: 009 / Book Number: 083 / Hadith Number: 47
Narrated Abu Huraira:
Allah's Apostle said, "There is no Diya for persons killed by animals or for the one who has been killed accidentally by falling into a well or for the one killed in a mine. And one-fifth of Rikaz (treasures buried before the Islamic era) is to be given to the state."