Sahih Muslim 1686
صحيح مسلم#1686SahihA'isha reported that the Apostle (ﷺ) was not so much particular about observing supererogatory rak'ahs as in case of the two rak'ahs of the dawn prayer
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: 6:116