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 (c. AD 15–100) Greek philosopher and religious leader [Ἀπολλώνιος]

Letters from Apollonius of Tyana, ep. 15, Letter to Euphrates [tr. Jones (2006)]
    (Source)

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