Abu al-Zinad (may Allah have mercy on him) said that Umar bin Abd al-Aziz (may Allah have mercy on him) wrote to Abd al-Hamid bin Abd al-Rahman bin Zayd bin al-Khattab (may Allah have mercy on him), who was the governor of Kufah, that he should judge by an oath and a witness.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20678