Kautilya's Arthashastra 7.8.18

7.8.18

mitrād ātmavṛddhiṃ hi prāpnoti, kṣayavyayapravāsaparopakārān itaraḥ //

Of the two, the conqueror and his enemy, both of whom may happen to have a friend in the same person, he who helps a true or a truer friend overreaches the other; for, by helping a true friend, he enriches himself, while the other not only incurs loss of men and money and the hardships of sojourning abroad, but also showers benefits on an enemy who hates the benefactor all the more for his gratification.