The Republic by Plato Part 1 Page 44

interest, and that for subjects to obey them is justice.

Yes, Polemarchus, — Thrasymachus said that for subjects to do what was commanded by their rulers is just.

Yes, Cleitophon, but he also said that justice is the interest of the stronger, and, while admitting both these propositions, he further acknowledged that the stronger may command the weaker who are his subjects to do what is not for his own interest; whence follows that justice is the injury quite as much as the interest of the stronger.

But, said Cleitophon, he meant by the interest of the stronger what the stronger thought to be his interest, — this was what the weaker had to do; and this was affirmed by him to be justice.

Those were not his words, rejoined Polemarchus.