Does anybody know where this expression comes from? It has always seemed rather biblical to me, but I suppose it could just be referring to some generic Peter and Paul...

Ive thought about this myself and come to the conclusion that there is no Biblical allusion, two common names were chosen which are alliterative to make the saying more striking.

Here is one more sample of what can be found by typing words into Yahoo search box. Do it, and up come a whole bunch of links, one of which explains that it arose out of a somewhat complicated theological discussion, which I was too lazy to try to understand.