Where did “Cleanliness is next to Godliness” originate?

John Wesley in one of his sermons indicated that the proverb was already well known in the form we use today. Wrote Wesley: 'Slovenliness is no part of religion.'Cleanliness is indeed next to Godliness.

(from PhraseFinder, which has a useful entry too long to quote)

It was my understanding that the adage "cleanliness is next to Godliness" had nothing to do with piety. It was explained to me that the expression began during the time of the black plague in mid-14th century, and was an expression listing what should be a person's priorities. Godliness should be at the top of a person's priorities, closely followed by cleanliness. It wouldn't surprise me at all if Nostradamus coined the phrase.