Qur'an 47:4

فَإِذَا لَقِيتُمُ ٱلَّذِينَ كَفَرُوا۟ فَضَرْبَ ٱلرِّقَابِ حَتَّىٰٓ إِذَآ أَثْخَنتُمُوهُمْ فَشُدُّوا۟ ٱلْوَثَاقَ فَإِمَّا مَنًّۢا بَعْدُ وَإِمَّا فِدَآءً حَتَّىٰ تَضَعَ ٱلْحَرْبُ أَوْزَارَهَا ۚ ذَٰلِكَ وَلَوْ يَشَآءُ ٱللَّهُ لَٱنتَصَرَ مِنْهُمْ وَلَـٰكِن لِّيَبْلُوَا۟ بَعْضَكُم بِبَعْضٍ ۗ وَٱلَّذِينَ قُتِلُوا۟ فِى سَبِيلِ ٱللَّهِ فَلَن يُضِلَّ أَعْمَـٰلَهُمْ

Now when ye meet in battle those who disbelieve, then it is smiting of the necks until, when ye have routed them, then making fast of bonds; and afterward either grace or ransom till the war lay down its burdens. That (is the ordinance). And if Allah willed He could have punished them (without you) but (thus it is ordained) that He may try some of you by means of others. And those who are slain in the way of Allah, He rendereth not their actions vain.