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Don Quixote by Miguel de Cervantes, which predates Tolkien by a couple centuries or so, and from whom the bloviating Englishman stole that line:
"'Tis an old saying, the Devil lurks behind the cross. All is not gold that glitters."
I believe William Blake also used a similar line, but substituted "glisters" for "glistens."
I figured the second verse identified it as JRRT. I should have listed the author. My bad. : ^ )