Whenever Messenger of Allah ﷺ came out on ʿId 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).  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا خَرَجَ يَوْمَ الْعِيدِ أَمَرَ بِالْحَرْبَةِ فَتُوضَعُ بَيْنَ يَدَيْهِ فَيُصَلِّي إِلَيْهَا وَالنَّاسُ وَرَاءَهُ وَكَانَ يَفْعَلُ ذَلِكَ فِي السَّفَرِ فَمِنْ ثَمَّ اتَّخَذَهَا الأُمَرَاءُ  

When the Messenger of Allah (may peace he upon him) went out on the 'Id day, he ordered to carry a spear-and it was fixed in front of him, and he said prayer towards its (direction), and the people were behind him. And he did it in the journey, and that is the reason why the Amirs carried it.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا خَرَجَ يَوْمَ الْعِيدِ أَمَرَ بِالْحَرْبَةِ فَتُوضَعُ بَيْنَ يَدَيْهِ فَيُصَلِّي إِلَيْهَا وَالنَّاسُ وَرَاءَهُ وَكَانَ يَفْعَلُ ذَلِكَ فِي السَّفَرِ فَمِنْ ثَمَّ اتَّخَذَهَا الأُمَرَاءُ  

When the Messenger of Allah ﷺ would go out (for prayer) on the day of 'Id, he ordered to bring a lance, it was then setup in front of him and he would pray in its direction, and the people (stood) behind him. He used to do so during journey ; hence the rulers would take it (lance with them). (Using translation from Abū Dāʾūd 687)  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا خَرَجَ يَوْمَ الْعِيدِ يَأْمُرُ بِالْحَرْبَةِ فَتُوضَعُ بَيْنَ يَدَيْهِ فَيُصَلِّي إِلَيْهَا وَالنَّاسُ وَرَاءَهُ وَكَانَ يَفْعَلُ ذَلِكَ فِي السَّفَرِ فَمِنْ ثَمَّ اتَّخَذَهَا الْأُمَرَاءُ  

[Machine] The Messenger of Allah ﷺ used to command the warriors when he went out on the day of Eid, and it would be placed in front of him, and he would pray towards it with the people behind him. And he used to do this during travels, so the rulers thereafter adopted it.  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا خَرَجَ يَوْمَ الْعِيدِ أَمَرَ بِالْحَرْبَةِ فَتُوضَعُ بَيْنَ يَدَيْهِ فَيُصَلِّي إِلَيْهَا وَالنَّاسُ وَرَاءَهُ وَكَانَ يَفْعَلُ ذَلِكَ فِي السَّفَرِ فَمِنْ ثَمَّ اتَّخَذَهَا الْأُمَرَاءُ