Aristotle, The Art of Rhetoric 3.15.1416a13 = T 165 Radt
ἄλλος τόπος, ὡς ἔστιν ἁμάρτημα ἢ ἀτύχημα ἢ ἀναγκαῖον· οἷον Σοφοκλῆς ἔφη τρέμειν οὐχ ὡς ὁ διαβάλλων ἔφη, ἵνα δοκῆι γέρων, ἀλλ’ ἐξ ἀνάγκης. οὐ γὰρ ἑκόντι εἶναι αὑτῶι ἔτη ὀγδοήκοντα.
Another topic (sc. relating to the disarming of slander): that it was a mistake or misfortune or necessity. Sophocles, for example, said that he was trembling not, as his slanderer said, so that he would appear old, but out of necessity. For he was not eighty years old by choice.