idle hands are the devil's workshop
Definition from Wiktionary, the free dictionary
See also: idle hands are the Devil's workshop
- Idle hands are the devil's playthings
- Idle hands are the devil's tools
- the devil makes work for idle hands
- any of these, but with Devil in place of devil
Probably ultimately from St. Jerome's saying: fac et aliquid operis, ut semper te diabolus inveniat occupatum.