Sahih Bukhari Volume 1, Book 9, Hadith Number 473

Narated By Ibn ‘Umar : Whenever Allah’s Apostle 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 , this practice was adopted by the Muslim rulers (who followed his traditions).