Sunan Ibn Majah, Chapter: The Chapters on Jihad

"When Mughirah bin Shu'bah fought alongside the Prophet (saw) he would carry a spear, and when he would come back he would throw his spear down so that someone would pick it up and give it back to him." Ali said to him: "I will tell the Messenger of Allah (saw) about that." He (the Prophet (saw)) said: "Do not do that, for it you do that it will not be picked up as a lost item to be returned."