Plato, Letters 323a

μήπω συγγεγονότι, καὶ τέχνῃ διʼ ἐμπειρίας εἰληφέναι. τί οὖν δὴ λέγω; σοὶ μέν, Ἑρμεία, πεπειραμένος Ἐράστου καὶ Κορίσκου πλέονα ἢ σύ, φημὶ καὶ μηνύω καὶ μαρτυρῶ μὴ ῥᾳδίως εὑρήσειν σε ἀξιοπιστότερα ἤθη τούτων τῶν γειτόνων· ἔχεσθαι δὴ παντὶ συμβουλεύω δικαίῳ τρόπῳ τούτων τῶν ἀνδρῶν, μὴ πάρεργον ἡγουμένῳ. Κορίσκῳ δὲ καὶ Ἐράστῳ πάλιν Ἑρμείου ἀντέχεσθαι σύμβουλός εἰμι καὶ πειρᾶσθαι ταῖς

so far as I can judge without having met him as yet—to possess this practical ability both by nature and also through the skill bred of experience. What, then, do I suggest? To you, Hermeias, I, who have made trial of Erastus and Coriscus more fully than you, affirm and proclaim and testify that you will not easily discover more trustworthy characters than these your neighbors; and I counsel you to hold fast to these men by every righteous means, and regard this as a duty of no secondary importance. To Coriscus and Erastus the counsel I give is this—that they in turn should hold fast to Hermeias,