Plato, Letters 310d

λέγειν τὸν ἕτερον ὅτι ἀκούοι Ὀλυμπίασι πολλῶν τινων τῶν μετʼ ἐμοῦ σε κακηγορούντων. ἴσως γὰρ ὀξύτερον ἐμοῦ ἀκούει· ἐγὼ μὲν γὰρ οὐκ ἤκουσα. χρὴ δέ, ὡς ἐμοὶ δοκεῖ, οὑτωσί σε ποιεῖν τοῦ λοιποῦ, ὅταν τι τοιοῦτον λέγῃ τις περὶ ἡμῶν τινος, γράμματα πέμψαντα ἐμὲ ἐρέσθαι· ἐγὼ γὰρ τἀληθῆ λέγειν οὔτε ὀκνήσω οὔτε αἰσχυνοῦμαι. ἐμοὶ δὲ δὴ καὶ σοὶ τὰ πρὸς ἀλλήλους οὑτωσὶ τυγχάνει ἔχοντα· οὔτε αὐτοὶ ἀγνῶτές ἐσμεν οὐδενὶ Ἑλλήνων ὡς ἔπος

one of these men declares that at Olympia he heard quite a number of my companions maligning you. No doubt his hearing is more acute than mine; for I certainly heard no such thing. For the future, whenever anyone makes such a statement about any of us, what you ought, I think, to do is to send me a letter of inquiry; for I shall tell the truth without scruple or shame. Now as for you and me, the relation in which we stand towards each other is really this. There is not a single Greek, one may say, to whom we are unknown, and our intercourse is a matter of common talk;