Plato, Letters 314c

οὐ γὰρ ἔστιν τὰ γραφέντα μὴ οὐκ ἐκπεσεῖν. διὰ ταῦτα οὐδὲν πώποτʼ ἐγὼ περὶ τούτων γέγραφα, οὐδʼ ἔστιν σύγγραμμα Πλάτωνος οὐδὲν οὐδʼ ἔσται, τὰ δὲ νῦν λεγόμενα Σωκράτους ἐστὶν καλοῦ καὶ νέου γεγονότος. ἔρρωσο καὶ πείθου, καὶ τὴν ἐπιστολὴν ταύτην νῦν πρῶτον πολλάκις ἀναγνοὺς κατάκαυσον.ταῦτα μὲν ταύτῃ. περὶ δὲ Πολυξένου ἐθαύμασας ὅτι

for it is not possible that what is written down should not get divulged. For this reason I myself have never yet written anything on these subjects, and no treatise by Plato exists or will exist, but those which now bear his name belong to a Socrates become fair and young. Fare thee well, and give me credence; and now, to begin with, read this letter over repeatedly and then burn it up. So much, then, for that. You were surprised at my sending Polyxenus to you; but now as of old I repeat