Martial, Epigrams 4.21
nullos esse deos, inane caelum
adfirmat Segius: probatque, quod se
factum, dum negat haec, videt beatum.
Segius asserts that there are no gods, that heaven is empty. And he’s the proof, because, even as he denies these things, he sees that he’s become prosperous.
A slightly convoluted logical argument, explained here by the great JP Sullivan.