The Oxford Dictionary of Quotations, the Oxford Dictionary of Modern Quotations, and Wikiquote, all have a selection of remarks attributed to W. C. Fields; but this one is not amongst any of them.
You can find it on any number of other websites, including BrainyQuote (which I am not even going to dignify with a link). This is far from the first time that I've written on this website, words to the effect of "Please do not use quotations from BrainyQuote, unless you can verify it somewhere else that's more reliable."
The same goes for GoodReads, which seems to get all its quotes from BrainyQuote. And for Pinterest, of which the same could be said.
© Macclesfield Quiz League 2020