Musnad Ahmad 30:1884

Bahz narrated to us, Hammad narrated to us, from Muhammad, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "The animal (al-ajma') is a liability (jubar), the well is a liability (jubar), and the mine is a liability (jubar). And in the buried treasure (rikaz), there is one-fifth."