Plato said that virtue has no master. If a person does not honor this principle and rejoice in it, but is purchasable for money, he creates many masters for himself.

Apollonius of Tyana
Apollonius of Tyana (c. AD 15-100) Greek philosopher and religious leader [Ἀπολλώνιος]
Letters from Apollonius of Tyana, ep. 15, Letter to Euphrates [tr. Jones (2006)]

The reference to Plato's Republic, X 617 E.