the devil finds work for idle hands to do

Definition 
Idle people may find themselves tempted into wrongdoing: "There is a risk that youngsters will leave school and college to find themselves unwanted, with the devil finding work for idle hands to do" (London Times, 1980). The proverb comes from a poem by Isaac Watts, published in his Divine Songs for Children (1715): "In works of labour, or of skill,/I would be busy too;/ For Satan finds some mischief still/For idle hands to do." In Charles Dickens's novel David Copperfield (1850), the character Mr. Wickfield observes, "if Doctor Watts knew mankind, he might have written, with as much truth, 'Satan finds some mischief still, for busy hands to do.' The busy people achieve their full share of mischief in the world, you may rely upon it."