Lucian, Slander 8
Lucian quotes a hexameter from ‘the best of poets’; the scholiast claims it is by Phocylides, but it’s quoted by various other authors, and is elsewhere attributed to Hesiod.
εἰ δέ τῳ μὴ ἀξιόπιστοι δοκοῦσιν οἱ νομοθέται παραινοῦντες οὕτω δικαίας καὶ ἀμερεῖς ποιεῖσθαι τὰς κρίσεις, ποιητήν μοι δοκῶ τὸν ἄριστον ἐπάγειν τῷ λόγῳ εὖ μάλα περὶ τούτων ἀποφηνάμενον, μᾶλλον δὲ νομοθετήσαντα. φησὶ δέ,
μήτε δίκην δικάσῃς, πρὶν ἄμφω μῦθον ἀκούσῃς.
If anyone thinks that the lawgivers, who recommend that verdicts be given justly and impartially, are not worthy of our trust, I have a mind to quote the best poet, who gave an excellent opinion – or rather laid down the law – on these matters. He says:
Do not give your judgement until you have heard a speech on both sides.