Surah 47

Surah 47:4

"When you meet those who disbelieve, (let there be) a striking of the necks, until, when you have subdued them, bind (them) securely, and then either (set them free) as a favor or by ransom, until the war lays down its burdens. That (is the rule). If God had (so) pleased, He would indeed have defended Himself against them, but (He allows fighting) so that He may test some of you by means of others. Those who are killed in the way of God – He will not lead their deeds astray."