Sahih al-Bukhari 1163
صحيح البخاري#1163SahihNarrated `Aisha:The Prophet (ﷺ) was never more regular and particular in offering any Nawafil than the two rak`at (Sunna) of the Fajr 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 al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 19:42