From Plautus' Pot of Gold: the miser Euclio, whose buried treasure has almost been found, calls on Apollo.

The formula is a genuine one, and the joke is in the third line. Si cui in re tali iam subvenisti antidhac — "if you have ever helped anyone in such a case before". A Roman prayer ordinarily reminds the god of past benefits as grounds for a new one: you have helped, so help again. Euclio has nothing to cite and therefore builds his condition on speculation: perhaps there was a precedent.

Plautus is not parodying piety here. He is showing a man who has no history of relations with the gods at all — and who knows it.