Musnad Abu Ya'la al-Mawsili 3:51

Ubayd Allah narrated to us, Muhammad ibn Abd Allah ibn al-Zubayr narrated to us, Sufyan narrated to us, from Abu Ishaq, from Abu al-Khalil, from Ali, who said: Al-Mughirah 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 plant it in the ground, and people would pass by it and carry it. He said: I said, "I will surely inform the Messenger of Allah (may Allah bless him and grant him peace) about it." He said, "Then a lost item will not be picked up." So I left it.