Sahih Muslim 2728
صحيح مسلم#2728SahihAnas (Allah be pleased with him) reported that the Messenger of Allah (ﷺ) used to observe fast till it was said that he had observed fast, he had observed fast (perhaps never to break it), and he did not fast till it was said that he had given up fast, he had given up fast (perhaps never to observe it)
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: 13:234