https://en.wiktionary.org/wiki/idle_hands_are_the_devil%27s_workshop

Proverbs 16:27 "Scoundrels concoct evil, and their speech is like a scorching fire." (Oxford, NSRV, 5th Edition) is translated in the King James version as "An ungodly man diggeth up evil: and in his lips there is as a burning fire." The Living Bible (1971) translates this section as "Idle hands are the devil’s workshop; idle lips are his mouthpiece."

The verse may have inspired St. Jerome to write "fac et aliquid operis, ut semper te diabolus inveniat occupatum" (translation: "engage in some occupation, so that the devil may always find you busy.”) This was repeated in The Canterbury Tales which may have increased its popularity.