Sahih al-Bukhari 494
Narrated Ibn `Umar:
Whenever Allah's Messenger (ﷺ) came out on `Id day, he used to order that a Harba [??] (a short spear) to be 
planted in front of him (as a Sutra for his prayer) and then he used to pray facing it with the people 
behind him and used to do the same while on a journey. After the Prophet (ﷺ) , this practice was adopted 
by the Muslim rulers (who followed his traditions).
حَدَّثَنَا إِسْحَاقُ، قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، قَالَ حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا خَرَجَ يَوْمَ الْعِيدِ أَمَرَ بِالْحَرْبَةِ فَتُوضَعُ بَيْنَ يَدَيْهِ، فَيُصَلِّي إِلَيْهَا وَالنَّاسُ وَرَاءَهُ، وَكَانَ يَفْعَلُ ذَلِكَ فِي السَّفَرِ، فَمِنْ ثَمَّ اتَّخَذَهَا الأُمَرَاءُ‏.‏