>>What is the source for that comment?<<
I don’t know. It looks like that post was pulled but if I remember it claimed a source as a book. It looks like you can download the book and read it yourself here:
http://www.manybooks.net/titles/stapletonj1843818438.html
No the book is not at that website. I found other sources for that quote from a number of anti-Catholic websites. You’ll pardon me if I don’t take your non-authoritative word for it.