Sunan Ibn Majah Book 5, Hadith 140
“The Messenger of Allah had a reed
mat that he would spread out during the day, and make into a
compartment at night, towards which he would perform prayer.”
“A small spear (Harbah) would be brought out to the Prophet (ﷺ) when he was travelling; he would plant it (in the ground) to perform prayer while facing it.”
“When anyone of you performs prayer, let him put something in front of him. If he cannot find anything then let him put a stick. If he cannot find one, then let him draw a line. Then it will not matter if anything passes in front of him.”