Sahih Muslim 1700
صحيح مسلم#1700SahihA'isha reported that the Messenger of Allah (ﷺ) would pray in the night for a long time, and when he prayed standing be bowed in a standing posture, and when he prayed sitting, he bowed in a sitting posture
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: 6:130