Sahih Muslim 1710
صحيح مسلم#1710SahihA'isha reported that the Messenger of Allah (ﷺ) died (in this very state) that he observed most of his (Nafl) prayers in a sitting 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: 6:140