Lactantius, Divine Institutes
3.24.10 (tr. Mary Francis McDonald):
I do not know what to say about those who, when once
they have gone astray, constantly remain in their foolishness
and defend their empty theses with empty prattling, except
that sometimes I think that they philosophize for the sake of
a joke, or that cleverly and knowingly they take up lies to
defend them, so that they might, as it were, exercise or demonstrate their abilities in evil things.
quid dicam de his nescio, qui cum semel
aberraverint, constanter in stultitia perseverant et vanis vana defendunt, nisi quod eos interdum puto aut ioci causa philosophari
aut prudentes et scios mendacia defendenda suscipere, quasi ut
ingenia sua in malis rebus exerceant vel ostendant.