Sahih al-Bukhari 1160
صحيح البخاري#1160SahihNarrated `Aisha:The Prophet (ﷺ) used to lie down on his right side, after offering 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: 19:39