SB 1.7.36

mattaṁ pramattam unmattaṁ
 suptaṁ bālaṁ striyaṁ jaḍam
prapannaṁ virathaṁ bhītaṁ
 na ripuṁ hanti dharma-vit
Word for word: 
mattam — careless; pramattam — intoxicated; unmattam — insane; suptam — asleep; bālam — boy; striyam — woman; jaḍam — foolish; prapannam — surrendered; viratham — one who has lost his chariot; bhītam — afraid; na — not; ripum — enemy; hanti — kill; dharma-vit — one who knows the principles of religion.
Translation: 
A person who knows the principles of religion does not kill an enemy who is careless, intoxicated, insane, asleep, afraid or devoid of his chariot. Nor does he kill a boy, a woman, a foolish creature or a surrendered soul.
Purport: 

An enemy who does not resist is never killed by a warrior who knows the principles of religion. Formerly battles were fought on the principles of religion and not for the sake of sense gratification. If the enemy happened to be intoxicated, asleep, etc., as above mentioned, he was never to be killed. These are some of the codes of religious war. Formerly war was never declared by the whims of selfish political leaders; it was carried out on religious principles free from all vices. Violence carried out on religious principles is far superior to so-called nonviolence.