From Sahih Bukhari (Hadith 6912):
Narrated Abu Huraira:Allah's Messenger (ﷺ) 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
Reference: Bukhari 6912