Plato, Laws 723b

γε τὸν ἐμὸν λόγον τοῦτʼ αὐτό, προοίμιον, ἀλλʼ οὐ λόγος ἂν ὀρθῶς προσαγορεύοιτο εἶναι τοῦ νόμου. ταῦτʼ οὖν εἰπών, τί τὸ μετὰ τοῦτο ἄν μοι βουληθείην εἰρῆσθαι; τόδε, ὡς τὸν νομοθέτην πρὸ πάντων τε ἀεὶ τῶν νόμων χρεών ἐστιν μὴ ἀμοίρους αὐτοὺς προοιμίων ποιεῖν καὶ καθʼ ἕκαστον, ᾗ διοίσουσιν ἑαυτῶν ὅσον νυνδὴ τὼ λεχθέντε διηνεγκάτην. τό γʼ ἐμὸν οὐκ ἂν ἄλλως νομοθετεῖν διακελεύοιτο ἡμῖν τὸν τούτων ἐπιστήμονα.

the right term for it would be, not legal statement, but prelude, and no other word. Having said this, what is the next statement I would desire to make? It is this: that the lawgiver must never omit to furnish preludes, as prefaces both to the laws as a whole and to each individual statute, whereby they shall surpass their original form by as much as the double examples recently given surpassed the single. I, for my part, would charge the expert in these matters to legislate thus, and not otherwise.