Sulaiman bin Hayan al-Azdi سليمان بن حيان الأزدي · The Book on Salat (Prayer)

"I was with my father at the plains of Namirah. I passed by a mount and saw Allah's Messenger standing in Salat." He said: "I was looking at the earthiness of his armpits when he prostrated." : "Whiteness."

"The Prophet performed Salat towards his she-camel, or his mount, and he would perform Salat while on his mount, whichever direction it was facing."