Musnad Abu Ya'la al-Mawsili 110:185

Muhammad ibn Abdullah ibn Numayr narrated to us, Zayd ibn al-Hubab narrated to us, Sayf ibn Sulayman narrated to us, he said: Qays ibn Sa'd narrated to me, from Amr ibn Dinar, from Ibn Abbas, that the Prophet (may Allah bless him and grant him peace) judged by an oath and a witness.