Isma'il bin Amr bin Qays bin Sa'd bin Ubadah (may Allah have mercy on him) narrates from his father that they found in the writing of Sayyiduna Sa'd bin Ubadah (may Allah be pleased with him): the Messenger of Allah (peace and blessings be upon him) gave judgement on the basis of an oath together with a single witness. These are the words of the narration of Ibn Abi Uways.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5343