Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: "This verse was revealed specifically regarding voluntary prayers, meaning that whichever direction your mount faces, you may perform prayer facing that way."
Hadith Referenceسنن الدارقطني / كتاب الصلاة / 1063
Hadith Takhrij«أخرجه الدارقطني فى ((سننه)) برقم: 1063 ، انفرد به المصنف من هذا الطريق»