Volume 2 · Book 15 · Hadith 89
Narrated Ibn Umar: On the day of 'Id-ul-Fitr and 'Id-ul-Adha a spear used to be planted in front of the Prophet I (as a Sutra for the prayer) and then he would pray.
— Sahih Bukhari, Volume 2, Book 15: The Two Festivals (Eids), Hadith #89