Musnad Ahmad 5:705

Abu Ahmad narrated to us, Sufyan narrated to us, from Abu Ishaq, from Abu al-Khalil, from Ali, who said: Al-Mughirah ibn Shu'bah had a spear, and whenever we went out with the Messenger of Allah, may Allah bless him and grant him peace, on a military expedition, he would take it with him. He would plant it in the ground, and people would pass by it and carry it. I said: "If I come to the Prophet, may Allah bless him and grant him peace, I will inform him." He said: "If you do that, you will not return a lost item."