Musannaf Ibn Abi Shayba 20:61

Abu Bakr narrated to us, he said: Fadl ibn Dukayn narrated to us, from Isra'il, from Simak, from 'Ikrimah, from Ibn 'Abbas, he said: The Messenger of Allah (may Allah bless him and grant him peace) decreed regarding buried treasure (rikaz) the fifth.