Sahih Muslim 1665
صحيح مسلم#1665SahihMua'ada 'Adawiyya reported 'A'isha as saying:The Messenger of Allah (ﷺ) used to observe four rak'ahs in the forenoon prayer and he sometimes observed more as Allah pleased
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: 6:95