Volume 3 · Book 40 · Hadith 545
Narrated Abu Huraira: Allah's Apostle said, "No bloodmoney will be charged if somebody dies in a mine or in a well or is killed by an animal; and if somebody finds a treasure in his land he has to give one-fifth of it to the Government."
— Sahih Bukhari, Volume 3, Book 40: Distribution of Water, Hadith #545