Amr bin Dinar narrates from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) "gave judgment with an oath along with a witness." Amr says: (This was) regarding property.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20635