from Allah, and his refuge is Hell—what an evil destination!” [Al-Anfal 8:16]
The Prophet, peace and blessings be upon him, also informed us that fleeing on the day of battle is among the grave, destructive sins, saying: “Avoid the seven destructive sins,” and he mentioned among them “fleeing on the day of battle.” (1) However, Allah, Exalted is He, made two exceptions:
The first is that he may be maneuvering for battle—that is, withdrawing in order to carry out a combat tactic. For example, he may draw his enemy onward, then, when the enemy catches up with him, turn upon him and kill him.
The second is that he may be joining another group: for instance, he may learn that a group of Muslims on the other side is close to being defeated, so he goes to join them in order to reinforce them. In this case, however, it is conditional that he does not fear for the group he is leaving behind. If he fears for that group, then he is not permitted to go to the other group. In that case, it becomes an individual obligation upon him, and he is not permitted to withdraw from it.
His statement, “or when an enemy besieges his town”: this is the second circumstance. When an enemy besieges his town, he must fight in defense of it. This resembles the case of one who is present in the battle line, for when the enemy lays siege to a town, it will prevent people from leaving it, entering it, and receiving provisions and other necessities known to be affected by a siege. In this situation, the inhabitants of the town must fight in defense of their town.