Musnad Ahmad 30:1850

Hashim ibn al-Qasim narrated to us, Abu Ja'far—meaning al-Razi—narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The beast is [a cause of] 'jibar' (no liability), the well is [a cause of] 'jibar', and the mine is [a cause of] 'jibar'. And in the buried treasure (rikaz), there is one-fifth."