Sahih Muslim 2518
صحيح مسلم#2518SahihAbu Huraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as saying:Do not observe fast for a day, or two days ahead of Ramadan except a person who is in the habit of observing a particular fast; he may fast on that day
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: 13:24