Musnad Ahmad 30:3286

Abu Mu'awiyah narrated to us, he said: Muhammad ibn 'Amr narrated to us, from Abu Salamah, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The animal (al-'ajma') is a liability (jubar), and the well is a liability (jubar), and in buried treasure (al-rikaz) is one-fifth."