Musannaf Ibn Abi Shayba 18:1324

Abu Bakr narrated to us, he said: Ibn 'Uyaynah narrated to us, from 'Amr ibn Dinar, from 'Amr ibn Shu'ayb, from 'Abdullah ibn 'Amr, from the Prophet (may Allah bless him and grant him peace), who said: "Whoever is killed defending his wealth, then he is a martyr."