Against the Sophists (5-6)

But what is most ridiculous of all is that they distrust those from whom they are to get this money—they distrust, that is to say, the very men to whom they are about to deliver the science of just dealing—and they require that the fees advanced by their students be entrusted for safe keeping[*] to those who have never been under their instruction, being well advised as to their security, but doing the opposite of what they preach.

For it is permissible to those who give any other instruction to be exacting in matters open to dispute, since nothing prevents those who have been made adept in other lines of training from being dishonorable in the matter of contracts. But men who inculcate virtue and sobriety—is it not absurd if they do not trust in their own students before all others?[*] For it is not to be supposed that men who are honorable and just-dealing with others will be dishonest with the very preceptors who have made them what they are.