It was narrated from Ibn ‘Umar that the Messenger of Allah (ﷺ) used to set out for the praying place in the morning of the day of ‘Eid, and a small spear would be carried before him. When he reached the praying place, it would be set up in front of him, then he would pray facing it, and that was because the praying place was an open space in which there was nothing that could serve as a Sutrah*. *Sutrah (screen), meaning a barrier of some type.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا عِيسَى بْنُ يُونُسَ، ح وَحَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا الْوَلِيدُ بْنُ مُسْلِمٍ، قَالاَ حَدَّثَنَا الأَوْزَاعِيُّ، أَخْبَرَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ كَانَ يَغْدُو إِلَى الْمُصَلَّى فِي يَوْمِ الْعِيدِ وَالْعَنَزَةُ تُحْمَلُ بَيْنَ يَدَيْهِ فَإِذَا بَلَغَ الْمُصَلَّى نُصِبَتْ بَيْنَ يَدَيْهِ فَيُصَلِّي إِلَيْهَا وَذَلِكَ أَنَّ الْمُصَلَّى كَانَ فَضَاءً لَيْسَ فِيهِ شَىْءٌ يُسْتَتَرُ بِهِ .
sunnah.com