Plato, Meno 91b

ἀρετὴν σκόπει παρὰ τίνας ἂν πέμποντες αὐτὸν ὀρθῶς πέμποιΜΕΝ. ἢ δῆλον δὴ κατὰ τὸν ἄρτι λόγον ὅτι παρὰ τούτους τοὺς ὑπισχνουμένους ἀρετῆς διδασκάλους εἶναι καὶ ἀποφήναντας αὑτοὺς κοινοὺς τῶν Ἑλλήνων τῷ βουλομένῳ μανθάνειν, μισθὸν τούτου ταξαμένους τε καὶ πραττομένους; καὶ τίνας λέγεις τούτους, ὦ Σώκρατες; οἶσθα δήπου καὶ σὺ ὅτι οὗτοί εἰσιν οὓς οἱ ἄνθρωποι καλοῦσι σοφιστάς.

Now tell me, to whom ought we properly to send him for lessons in this virtue? Or is it clear enough, from our argument just now, that he should go to these men who profess to be teachers of virtue and advertise themselves as the common teachers of the Greeks, and are ready to instruct anyone who chooses in return for fees charged on a fixed scale? To whom are you referring, Socrates? Surely you know as well as anyone; they are the men whom people call sophists.