Sahih al-Bukhari 1105
صحيح البخاري#1105SahihNarrated Salim bin `Abdullah:Ibn `Umar said, "Allah's Messenger (ﷺ) used to pray the Nawafil on the back of his Mount (carriage) by signs facing any direction." Ibn `Umar used to do the same
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: 18:25