Sahih Muslim 2508
صحيح مسلم#2508SahihAbdullah b. 'Umar (Allah be pleased with both of them) reported Allah's Messenger (ﷺ) as saying:The month (of Ramadan) is thus and thus, and thus. i.e. ten, ten and nine
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: 13:14