Sayyiduna Abu Hurayrah (may Allah be pleased with him) says: "The Prophet (peace and blessings be upon him) gave judgment with an oath and one witness."
Abd al-Aziz said: I mentioned that to Suhayl, and he said: Rabi'ah, who is trustworthy in my view, informed me that I narrated it to him, but I do not remember it. Abd al-Aziz said: An illness had afflicted Suhayl which took away part of his mind, and he forgot some of his hadith; afterwards Suhayl used to narrate it from Rabi'ah, from himself, from his father.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20644