The Prophet ﷺ used to proceed to the Musalla and an 'Anaza used to be carried before him and planted in the Musalla in front of him and he would pray facing it (as a Sutra).  

كَانَ النَّبِيُّ ﷺ يَغْدُو إِلَى الْمُصَلَّى وَالْعَنَزَةُ بَيْنَ يَدَيْهِ تُحْمَلُ وَتُنْصَبُ بِالْمُصَلَّى بَيْنَ يَدَيْهِ فَيُصَلِّي إِلَيْهَا