Sahih Muslim 7126
صحيح مسلم#7126SahihA'isha reported that when Allah's Messenger (ﷺ) occupied himself in prayer, he observed such a (long) qiyam (posture of standing in prayer) that his feet were swollen. A'isha said:Allah's Messenger you do this (in spite of the fact) that your earlier and later sins have been pardoned for you? Thereupon, he said. A'isha should I not prove myself to be a thanksgiving servant (of Allah)?
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: 52:79