Aristotle, The Art of Rhetoric 1.14.1374b34 = T 164 Radt
καὶ εἰ ὁ παθὼν καὶ ἀδικηθεὶς αὐτὸς αὑτὸν μεγάλως ἐκόλασεν· ἔτι γὰρ μείζονι ὁ ποιήσας δίκαιος κολασθῆναι· οἷον Σοφοκλῆς ὑπὲρ Εὐκτήμονος συνηγορῶν, ἐπεὶ ἀπέσφαξεν ἑαυτὸν ὑβρισθεὶς, οὐ τιμήσειν ἔφη ἐλάττονος ἢ ὁ παθὼν ἑαυτῶι ἐτίμησεν.
And (the injustice is greater) if the one who has suffered and been wronged inflicts a great punishment on himself. For it is just <in that case> for the perpetrator to receive a still greater punishment. For example, Sophocles, when pleading on behalf of Euctemon, after the latter had killed himself because of the outrageous treatment he had suffered, said that he would not adjudicate the penalty at less than the victim had inflicted on himself.