Musannaf Ibn Abi Shayba 18:1323

Abu Bakr narrated to us, he said: Ibn 'Uyaynah narrated to us, from al-Zuhri, from Talhah ibn 'Abd Allah, from Sa'id ibn Zayd, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever is killed defending his wealth, then he is a martyr."