Plato, Letters 309d

ἱκανῶς ὑπὸ σοῦ τεθεράπευμαι. καί μοι τὸ τοῦ Εὐριπίδου κατὰ καιρόν ἐστιν εἰπεῖν, ὅτι σοὶ πραγμάτων ἄλλων ποτὲ συμπεσόντων—εὔξῃ τοιοῦτον ἄνδρα σοι παρεστάναι. ὑπομνῆσαι δέ σε βούλομαι διότι καὶ τῶν ἄλλων τραγῳδοποιῶν οἱ πλεῖστοι, ὅταν ὑπό τινος ἀποθνῄσκοντα τύραννον εἰσάγωσιν, ἀναβοῶντα ποιοῦσιν—

Indeed, I may appropriately quote the verse of Euripides—that one day, when other fortunes befall you,Thou’lt pray for such a helper by thy side. And I desire to remind you that most of the other tragedians also, when they show a tyrant on the stage slaughtered by someone, represent him as crying out—