No one on his deathbed ever regretted having been a Catholic.
Attr. St. Thomas More
I’m not familiar enough with St. Thomas More’s works to apply an ear test to this.
- Google search: A bunch of unsourced “quotations.” Just to be on the safe side, I looked at all 60 hits for deathbed regret catholic thomas more (Google search is smart enough to find inflected forms of “regret”) to no avail. That is to say, I found the saying (confirming that Google did search for inflected forms), but no citations.
- Wikiquote: Not on his page, and he has no discussion page.
- Google Books search: I went with deathbed regretted thomas more as keywords. The oldest match is from 2005, in Thomas Woods’ How the Catholic Church Built Western Civilization.
- The Center For Thomas More Studies has a pleasant-appearing website with a search function. Searching failed to turn up the alleged saying.
- I searched the Internet Archive’s copy of Life and Writing of St. Thomas More. Since it was OCRed and not proofread, I checked independently for regret and for Catholic, without finding the saying in question.
- It’s not in William Roper’s Life of St. Thomas More.
Given that spelling was far from standardized in More’s time, and given that someone else could have preserved this as a saying rather than something that More himself wrote, it’s not impossible that he said it. But it’s also not evident to me that he did.