Musnad Ahmad 30:2353

Abu Mu'awiyah narrated to us, Yahya bin Sa'id narrated to us, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I have indeed intended not to remain behind from any expedition that goes out in the way of Allah, but I do not have that upon which I can carry them. And I would love to be killed in the way of Allah, then brought to life, then killed, then brought to life, then killed."