(3) باب مَنْ حَفَرَ بِئْرًا فِي مِلْكِهِ لَمْ يَضْمَنْ
Narrated Abu Huraira:
Allah's Messenger (ﷺ) 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."
Reference: Sahih al-Bukhari 2355
In-book reference: Book 42, Hadith 5
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 40, Hadith 545