Musnad Ahmad 30:339

'Abd al-Razzaq narrated to us, Ibn Jurayj informed us, Ibn Shihab informed me, from Ibn al-Musayyib and Abu Salamah ibn 'Abd al-Rahman ibn 'Awf, from Abu Hurayrah, from the Messenger of Allah (may Allah bless him and grant him peace), who said: "The injury caused by an animal is exempt [from liability], the well is exempt [from liability], and the mine is exempt [from liability]. And in the buried treasure (rikaz), there is one-fifth."