Bg 2.19

ya enam vetti hantaram
yas cainam manyate hatam
ubhau tau na vijanito
nayam hanti na hanyate

Word for word: 
yah — anyone who; enam — this; vetti — knows; hantaram — the killer; yah — anyone who; ca — also; enam — this; manyate — thinks; hatam — killed; ubhau — both; tau — they; na — never; vijanitah — are in knowledge; na — never; ayam — this; hanti — kills; na — nor; hanyate — is killed.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Neither he who thinks the living entity the slayer nor he who thinks it slain is in knowledge, for the self slays not nor is slain.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When an embodied living entity is hurt by fatal weapons, it is to be known that the living entity within the body is not killed. The spirit soul is so small that it is impossible to kill him by any material weapon, as will be evident from subsequent verses. Nor is the living entity killable, because of his spiritual constitution. What is killed, or is supposed to be killed, is the body only. This, however, does not at all encourage killing of the body. The Vedic injunction is ma himsyat sarva bhutani: never commit violence to anyone. Nor does understanding that the living entity is not killed encourage animal slaughter. Killing the body of anyone without authority is abominable and is punishable by the law of the state as well as by the law of the Lord. Arjuna, however, is being engaged in killing for the principle of religion, and not whimsically.