Thanks to Google Books I found another Rabelais citation for this phrase:
"You'll teach me," said Panurge, "how to recognize flies when I see them floating in milk! By all that's holy, the man's a heretic. And I mean a fully developed heretic, a mangy heretic, a heretic who ought to be burned! His soul's going to be fried by thirty thousand cartloads of devils. And do you know where? By God, my friend, he's going to roast right under Queen Prosperpina's shitting stool, right in that infernal pot where she succumbs to the fecal workings of her suppositories, on the left-hand side of that great caldron, just three feet from Lucifer's claws, dragging him down into Demigorgon's black cave! Hah! the scoundrel!"