Musnad Ahmad 30:136

Sufyan narrated to us, from al-Zuhri, from Sa’id and Abu Salamah, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "The injury caused by an animal is exempt from liability (jubar), the mine is exempt from liability (jubar), and the well is exempt from liability (jubar). And in the buried treasure (rikaz), there is one-fifth."