Sahih al-Bukhari 1140
صحيح البخاري#1140SahihNarrated `Aisha:The Prophet (ﷺ) used to offer thirteen rak`at of the night prayer and that included the witr and 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: 19:21