سورة Muhammad - الآية 4

So when you confront the disbelievers, strike at their necks; until when you have slain them in plenty, tie them up firmly; then after that, you may either release them as a favour or take ransom, until the war lays down its ordeal; this is it; and had Allah willed He Himself could have taken revenge from them, but this is to test some of you with others; and Allah will surely never waste the deeds of those who were killed in His way.