Samyutta Nikaya III. 15
A man may plunder as long as it serves his ends, but when others are plundered, he who has plundered gets plundered in turn. A fool thinks, "Now's my chance," as long as his evil has yet to ripen. But when it ripens, the fool falls into pain. Killing, you gain your killer. Conquering, you gain one who will conquer you; insulting, insult; harassing, harassment. And so, through the cycle of action, he who has plundered gets plundered in turn.