Virtues of the Prayer Hall (Sutra of the Musalla)

Bukhari :: Book 1 :: Volume 9 :: Hadith 473

Narrated 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).