Sahih Muslim 1725
صحيح مسلم#1725SahihAbu Salama reported that he asked 'A'isha about the prayer of the Messenger of Allah (may peace he upon him) (during the night). The rest of the hadith is the same but with this exception that he (the Holy Prophet) observed nine rak'ahs including Witr
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 6:154