Musnad Ahmad 9:28

Sulayman ibn Dawud al-Hashimi narrated to us, Ibrahim ibn Sa'd narrated to us, from his father, from Abu Ubaydah ibn Muhammad ibn Ammar ibn Yasir, from Talhah ibn Abdullah ibn Awf, from Sa'id ibn Zayd, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever is killed defending his wealth is a martyr, and whoever is killed defending his family is a martyr, and whoever is killed defending his religion is a martyr, and whoever is killed defending his blood is a martyr."