Musnad Ahmad 90:1

Abu Amir Abd al-Malik ibn Amr narrated to us, Abd al-Aziz ibn al-Muttalib ibn Abdullah narrated to us, he said: My brother al-Hakam ibn al-Muttalib narrated to me, from his father, from Quhayd ibn Mutarrif al-Ghifari, that a questioner asked the Messenger of Allah, peace and blessings of Allah be upon him: "If an aggressor attacks me?" He commanded him to forbid him three times. He said: "What if he refuses?" He commanded him to fight him. He said: "And what about us?" He said: "If he kills you, you are in Paradise, and if you kill him, he is in the Fire."