Mishkat al-Masabih 6 Zakat كتاب الزكاة 27

وَعَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسلم: «العجماء جرحها جَبَّار والبشر جَبَّار والمعدن جَبَّار وَفِي الرِّكَاز الْخمس»

Abu Huraira reported God’s messenger as saying, “No retaliation is payable for a wound caused by a dumb animal, or for an accident in a well or a mine, but a fifth is payable on buried treasure.” * (Bukhari and Muslim.) * The word used (rikaz) is applied to treasure buried by people in pre-Islamic times; but the word may also mean metal in mines.