Sahih Muslim 2717
صحيح مسلم#2717SahihAbdullah b. Shaqiq reported:I said to'A'isha (Allah be pleased with her): Did the Messenger of Allah (ﷺ) fast for a full month besides Ramadan? She said: I do not know of any month in which he fasted throughout, but that of the month of Ramadan and (the month) in which he did not fast at all, till he ran the course of his life
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: 13:223