It is narrated from Sa'id bin Jubayr that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to offer (voluntary prayer) on his mount by gestures, whichever way the mount faced, and he would say: "the Prophet (peace and blessings be upon him) also used to do this." Then he recited this noble verse: "To Allah belong the east and the west; so wherever you turn, there is the Face of Allah. Indeed, Allah is All-Encompassing, All-Knowing." [Surah al-Baqarah: 115] Then he said: This verse was revealed concerning this very matter.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2201