Musnad Ahmad 30:3264

Muhammad ibn Ja‘far narrated to us, he said: ‘Awf narrated to us, from al-Hasan, he said: It reached me that the Messenger of Allah (may Allah bless him and grant him peace) said: "The mine is [a cause of] *jibar* (liability-free loss), the beast is [a cause of] *jibar*, and the well is [a cause of] *jibar*. And in the *rikaz* (buried treasure), there is one-fifth."