(10) باب صَلاَةِ التَّطَوُّعِ عَلَى الْحِمَارِ
Narrated Anas bin Seereen:
We went to receive Anas bin Malik when he returned from Sham and met him at a place called 'Ainat- Tamr. I saw him praying riding the donkey, with his face to this direction, i.e. to the left of the Qibla. I said to him, "I have seen you offering the prayer in a direction other than that of the Qibla." He replied, "If I had not seen Allah's Messenger (ﷺ) doing it, I would not have done it."
Reference: Sahih al-Bukhari 1100
In-book reference: Book 18, Hadith 20
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 20, Hadith 204