Musnad Abu Ya'la al-Mawsili 109:62

Amr narrated to us, Amr ibn Uthman al-Kilabi narrated to us, Harun ibn Hayyan narrated to us, Muhammad ibn al-Munkadir narrated to us, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace be upon him) said: "Whoever is killed defending his wealth, he is a martyr."