Sahih Muslim 1703
صحيح مسلم#1703SahihAbdullah b. Shaqiq al-'Uqaili reported:I asked 'A'isha about the prayer of the Messenger of Allah (ﷺ). She said: The Messenger of Allah (ﷺ) would observe prayer (Nafl) in a standing position as well as in a sitting position, and when he commenced the prayer in a standing position, he bowed in this very position, and when he commenced the prayer in a sitting position, he bowed in this very position
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: 6:133