Musnad Ahmad 28:353

'Abd al-Rahman narrated to us, from Sufyan, from 'Abd Allah ibn al-Hasan, from Ibrahim ibn Muhammad ibn Talhah, from 'Abd Allah ibn 'Amr, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever has his wealth sought [to be taken] without right, and he fights and is killed, then he is a martyr." And I think al-A'raj narrated to me, from Abu Hurayrah, the like of it.