CAPTIVES. Asir, pl. Usura, and Usara’. With respect to captives, the Imam, or leader of the army, has it in his choice to slay them, “because the Prophet put captives death, and also because slaying them terminates wickedness”; or he may if he choose make them slaves. It is not lawful for the Imam to send captives back to their home and country, because that would be to strengthen the cause of infidelity against Islam. If they become Muslims after their capture, they must not be put to death, but they may be sold after their conversion. A converted captive must not be suffered to return to his country, and it is not lawful to release a captive gratuitously. The only method of dividing plunder which consists of slaves, is by selling them at the end of the expedition and then dividing the money (Hidayah, ii. 160.) [SLAVERY.]
Based on Hughes, Dictionary of Islam