I also transmitted from the legal questions of Abū ʿAbd Allāh al-Naysābūrī at Ṭālaqān, from Aḥmad, that he was asked about the belligerent enemies: “If they take hostages from the Muslims and give us a hostage, then kill our hostage, may we kill their hostage as they did?” It seems that he held that their hostage should be killed.
The evidence that hostages are not to be killed is the report that the Prophet (peace and blessings be upon him) said: “Return the trust to the one who entrusted you, and do not betray the one who betrays you.” It is also related that the Byzantines violated their covenant during the time of Muʿāwiyah, while he held hostages in his custody. All the Muslims refrained from killing them and released them, saying: “Keeping faith despite treachery is better than answering treachery with treachery.”
If it is not permissible to kill hostages, their release is not obligatory unless we wage war against them. If we fight them, it becomes obligatory to release their hostages and escort them to a place of safety. It is permissible to stipulate in the truce contract that any of their men who embrace Islam be returned, provided there is no fear for their safety upon their return. If their safety cannot be assured, it is not permissible to return them to their people. Nor is it permissible to return any of their women who embrace Islam. If the return of a hostage is stipulated, it is not permissible to return a hostage.
If necessity does not require concluding a truce, it is not permissible to enter into a truce with them. However, it is permissible to agree to a four-month cessation of hostilities with them.
An individual grant of safe-conduct is valid whether issued by a man or a woman, a free person or a slave. Among the rulings governing this command is that the army commander may, when besieging the enemy, employ ballistae and mangonels against them. The Prophet (peace and blessings be upon him) set up a mangonel against the people of Taʾif. He may also demolish their dwellings over them, launch night raids against them, and use fire against them. If he deems it beneficial to cut down their date palms and trees, thereby weakening them so that he may overcome them or they may sue for peace,