Musnad Ahmad 25:1417

Al-Fadl ibn Dukayn narrated to us, Isma'il ibn Muslim al-'Abdi narrated to us, Abu al-Mutawakkil narrated to us, from Ibn 'Abbas: That he spent the night with the Prophet of Allah, may Allah bless him and grant him peace, one night. The Prophet of Allah, may Allah bless him and grant him peace, stood up during the night, went out, and looked at the sky. Then he recited this verse which is in Al 'Imran: {Indeed, in the creation of the heavens and the earth} [Al 'Imran: 190], until he reached: {Exalted are You; then protect us from the punishment of the Fire} [Al 'Imran: 191]. Then he returned to the house, used the siwak, performed ablution, then stood and prayed, then lay down. Then he returned again, looked at the sky, then recited this verse, then returned, used the siwak, and performed ablution, then stood and prayed, then lay down. Then he stood and went out, looked at the sky, then recited this verse, then returned, used the siwak, and performed ablution, then stood and prayed. *** Abu Ahmad narrated to us, Isra'il narrated to us, from Simak, from 'Ikrimah, from Ibn 'Abbas, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "In the Rikaz (buried treasure), there is one-fifth."