Plato, Letters 323c

φιλότητά τε καὶ κοινωνίαν, ἣν ἂν μὲν φιλοσοφῶμεν ἅπαντες ἡμεῖς τε καὶ ὑμεῖς, ὅσον ἂν δυνώμεθα καὶ ἑκάστῳ παρείκῃ, κύρια τὰ νῦν κεχρησμῳδημένα ἔσται. τὸ δὲ ἂν μὴ δρῶμεν ταῦτα οὐκ ἐρῶ· φήμην γὰρ ἀγαθὴν μαντεύομαι, καὶ φημὶ δὴ ταῦθʼ ἡμᾶς πάντʼ ἀγαθὰ ποιήσειν, ἂν θεὸς ἐθέλῃ.ταύτην τὴν ἐπιστολὴν πάντας ὑμᾶς τρεῖς ὄντας ἀναγνῶναι χρή, μάλιστα μὲν ἁθρόους, εἰ δὲ μή, κατὰ δύο, κοινῇ κατὰ δύναμιν ὡς οἷόν τʼ ἐστὶν πλειστάκις, καὶ χρῆσθαι συνθήκῃ

and fellowship. If, then, all of us—both we and you—practice this philosophy, as each is able, to the utmost of our power, the prophecy I have now made will come true; but if we fail to do this, I keep silence as to the consequence; for the prophecy I am making is one of good omen, and I declare that we shall, God willing, do all these things well. All you three must read this letter, all together if possible, or if not by twos; and as often as you possibly can read it in common, and use it as a form of covenant and a binding law,