Musnad Ahmad 30:2754

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, from Muhammad ibn Ziyad, he said: I heard Abu Hurairah saying: The Messenger of Allah, may Allah bless him and grant him peace, said: "The injury caused by an animal is exempt from liability (jubar), the well is exempt from liability (jubar), and the mine is exempt from liability (jubar), and in the buried treasure (rikaz) is one-fifth."