This is another article in the section Jihad from the classical manual on Sharia called Reliance of the Traveller. The articles are posted one by one in the order they are given in the book.
THE RULES OF WARFARE
o9 .10 It is not permissible (A: in Jihad) to kill women or children unless they are fighting against the Muslims. Nor is it permissible to kill animals, unless they are being ridden into battle against the Muslims, or if killing them will help defeat the enemy. It is permissible to kill old men (0: old man (shaykh) meaning someone more than forty years of age) and monks.
o9.11 It is unlawful to kill a non-Muslim to whom a Muslim has given his guarantee of protection (0: whether the non-Muslim is one or more than one, provided the number is limited, and the Muslim’s protecting them does not harm the Muslims, as when they are spies) provided the protecting Muslim has reached puberty, is sane, and does so voluntarily (0: and is not a prisoner of them or a spy).
o9.12 Whoever enters Islam before being captured may not be killed or his property confiscated, or his young children taken captive.
o9.13 When a child or a woman is taken captive, they become slaves by the fact of capture, and the woman’s previous marriage is immediately annulled.
o9.14 When an adult male is taken captive, the caliph (def: 025) considers the interests (0: of Islam and the Muslims) and decides between the prisoner’s death, slavery, release without paying anything, or ransoming himself in exchange for money or for a Muslim captive held by the enemy. If the prisoner becomes a Muslim (0: before the caliph chooses any of the four alternatives) then he may not be killed, and one of the other three alternatives is chosen.
o9.15 It is permissible in jihad to cut down the enemy’s trees and destroy their dwellings.