Isma'il bin Amr bin Qays bin Sa'd bin Ubadah narrates from his father that he found in the books of Sayyiduna Sa'd bin Ubadah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) "judged by an oath and a witness."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20663