Sahih Bukhari Volume 007, Book 072, Hadith Number 677.

Narrated By Abu Juhaifa : I saw Bilal bringing an 'Anza (a small spear) and fixing it in the ground, and then he proclaimed the Iqarna of the prayer, and I saw Allah's Apostle coming out, wearing a cloak with its sleeves rolled up. He then offered a two-Rak'at prayer while facing the 'Anza, and I saw the people and animals passing in front of him beyond the 'Anza.