Quotes Uncovered: Communism and Godliness

A while back, I invited readers to submit quotations for which they wanted me to try to trace the origins, using The Yale Book of Quotations and more recent research by me. Hundreds of people have responded via comments or e-mails. I am responding as best I can, a few per week.
Theodoric Meyer asked:

I’ve seen many variations on “If you have to ask, you’ll never know.” Who coined this expression?

The Yale Book of Quotations, which attempts to trace all famous quotations to their earliest occurrence, has the following:

[When asked to explain jazz:] “Lady, if you got to ask, you ain’t got it.” Thomas “Fats” Waller, Quoted in Washington Post, July 17, 1947. Often attributed to Louis Armstrong.

Rachel asked:

I would like to know the origin of a quote my dad and I often use: “The difference between communism and capitalism is that in capitalism, man exploits man. In communism, it’s the other way around.” I’ve seen it attributed to a variety of people, including John Kenneth Galbraith.

The YBQ has:

“Capitalism, it is said, is a system wherein man exploits man. And communism — is vice versa.” Daniel Bell, The End of Ideology (1960).

Elijah asked:

I have a quote that I’d like to know the origin of: “Cleanliness is next to Godliness.” Where is that from?

The Oxford Dictionary of Proverbs quotes John Wesley, Sermons on Several Occasions: “Cleanliness is, indeed, next to godliness.” Wesley put the phrase in quotation marks, as if it were an already existing saying.
Do any readers have any other quotations whose origins they would like me to attempt to trace?