Origin
The phrase is not in the Bible. Its conceptual ancestor is a sentence in a letter from Jerome to a young man named Rusticus (Letter 125, c. 411 CE): fac et aliquid operis, ut semper te diabolus inveniat occupatum — “always be doing some work, that the devil may always find you occupied.” This is the earliest documented form of the idea in Christian literature.
The idea passed into Middle English through Chaucer, who wrote in the Tale of Melibee (part of The Canterbury Tales, late 14th century) that idleness is the gate of all sin. Benjamin Franklin used variants in Poor Richard’s Almanack in the 18th century. The specific English wording “idle hands are the devil’s workshop” — sometimes “workplace,” “tools,” or “playground” — stabilised in 18th- and 19th-century English proverb collections.
The phrase is a Christian-traditional proverb. It is not a biblical citation.
What the Bible says about idleness
The Bible does address idleness — but with practical, community-oriented concerns rather than demonological framing. 2 Thessalonians 3:10-11 is the most direct passage: Paul tells the Thessalonian church that anyone unwilling to work should not eat, and notes that some are ataktōs (out of rank, disorderly) — living idly while creating disruption in the community.
The Greek ataktōs is a military image — a soldier out of formation. The concern in 2 Thessalonians is community function and personal discipline, not the metaphysical thesis that the devil takes up residence in idle people. The biblical concept and the proverb’s concept are related but not the same.
Proverbs 16:27 addresses the worthless man who digs up evil — a description of active mischief-making rather than passive idleness becoming dangerous. Ecclesiastes 10:18 names laziness as the cause of a house’s structural failure — a practical image, not a demonological one.