The Prophet ﷺ gave a decision on the basis of an oath and a single witness. Abu Dawud said: Al-Rabi' bin Sulaiman al-Mu'adhdhin told me some additional words in this tradition: Al-Shafi'i told me from 'Abd al-'Aziz. I then mentioned it fo Suhail who said: Rabi'ah told me - and he is reliable in my opinion - that I told him this (tradition) and I do not remember it. 'Abd al-'Aziz said: Suhail suffered from some disease which caused him to lose a little of his intelligence, and he forgot some of his traditions. Thereafter Suhail would narrate traditions from Rabi'ah on the authority of his father. (Using translation from Abū Dāʾūd 3610)   

أَنَّ رَسُولَ اللهِ ﷺ قَضَى بِالْيَمِينِ مَعَ الشَّاهِدِ الْوَاحِدِ