Narrated Ibn 'Umar:
"The Messenger of Allah (ﷺ) would perform voluntary Salat upon his mount facing whichever direction he was headed, while he was coming from Makkah to Al-Madinah." Then Ibn 'Umar recited: To Allah belong both the east and the west. (2:115)" And Ibn 'Umar said: "It was about this that the Ayah was revealed." (FR)
English reference (FR): Vol. 5, Book 44, Hadith 2958 (FR)
Arabic reference (FR): Book 47, Hadith 3217 (FR)