Lactantius

“ These are his own words: “God is one, but He who is one only does not need a name; for He who is self-existent is without a name.” God, therefore, has no name, because He is alone; nor is there any need of a proper name, except in cases where a multitude of persons requires a distinguishing mark, so that you may designate each person by his own mark and appellation. But God, because He is always one, has no peculiar name.
It remains for me to bring forward testimonies respecting the sacred responses and predictions, which are much more to be relied upon. ”

“ Also another Sibyl, whoever she is, when she said that she conveyed the voice of God to men, thus spoke:—
4. “I am the one only God, and there is no other God.”
I would now follow up the testimonies of the others, were it not that these are sufficient, and that I reserve others for more befitting opportunities. But since we are defending the cause of truth before those who err from the truth and serve false religions, what kind of proof ought we to bring forward [5] against them, rather than to refute them by the testimonies of their own gods? ”

“ For perhaps they against whom we are arguing may think that no credence is to be given to poets, as though they invented fictions, nor to philosophers, inasmuch as they were liable to err, being themselves but men. ”