From Sahih Bukhari (Hadith 376):
Narrated Abu Juhaifa:I saw Allah's Messenger (ﷺ) in a red leather tent and I saw Bilal taking the remaining water with which the Prophet had performed ablution. I saw the people taking the utilized water impatiently and whoever got some of it rubbed it on his body and those who could not get any took the moisture from the others' hands. Then I saw Bilal carrying a short spear (or stick) which he planted in the ground. The Prophet came out tucking up his red cloak, and led the people in prayer and offered two rak`at (facing the Ka`ba) taking a short spear (or stick) as a Sutra for his prayer. I saw the people and animals passing in front of him beyond the stick
Reference: Bukhari 376