Sahih Al Bukhari Hadith Number 972

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 (as a Sutra for the prayer) and then he would pray.

13  The Two Festivals (Eids)
Hadith number 972
Volume no 2
Chapter: 13 (As-Salat using a small spear as a Sutra)