حَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ، حَدَّثَنَا ابْنُ نُمَيْرٍ، عَنْ عُبَيْدِ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَإِذَا خَرَجَ يَوْمَ الْعِيدِ أَمَرَ بِالْحَرْبَةِ فَتُوضَعَ بَيْنَ يَدَيْهِ فَيُصَلِّي إِلَيْهَا وَالنَّاسُ وَرَاءَهُ وَكَانَ يَفْعَلُ ذَلِكَ فِي السَّفَرِ فَمِنْ ثَمَّ اتَّخَذَهَا الأُمَرَاءُ ‏.‏

Ibn 'Umar said

When the Messenger of Allah (ﷺ) went out on the day of 'Id, he would order that a spear be brought and placed in front of him, and he would pray facing it while the people were behind him. He used to do that while traveling, and consequently, the rulers adopted it.