فَإِذَا لَقِيتُمُ الَّذِينَ كَفَرُوا فَضَرْبَ الرِّقَابِ حَتَّىٰ إِذَا أَثْخَنْتُمُوهُمْ فَشُدُّوا الْوَثَاقَ فَإِمَّا مَنًّا بَعْدُ وَإِمَّا فِدَاءً حَتَّىٰ تَضَعَ الْحَرْبُ أَوْزَارَهَا

So, when you meet those who disbelieve strike at their necks till when you have killed and wounded many of them, then bind a bond firmly (i.e. take them as captives). Thereafter (is the time) either for generosity (i.e. free them without ransom), or ransom until the war lays down its burden (Muhammad 4).