The Prophet (ﷺ) used to pray (the Nawafil) on his Mount facing east and whenever he wanted to offer the compulsory prayer, he used to dismount and face the Qibla.
Reference: Sahih al-Bukhari 1099 In-book : Book 18, Hadith 19 USC-MSA web (English) : Vol. 2, Book 20, Hadith 203 (deprecated)
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