Aristotle, Nicomachean Ethics 3.2, 1111a8 = T93a Radt

ὃ δὲ πράττει ἀγνοήσειεν ἄν τις, οἷον λέγοντές φασιν ἐκπεσεῖν αὐτούς, ἢ οὐκ εἰδέναι ὅτι ἀπόρρητα ἦν, ὥσπερ Αἰσχύλος τὰ μυστικά…

But someone could be unaware of what he was doing, like those who say that something slipped out while they were speaking, or that they did not know that what they were saying was secret, like Aeschylus and the mysteries.

Relevant guides Aeschylus