Безделье - мать пороков

People who do not work learn to do wrong. See Лень до добра не доводит (Л), С личика - яичко, а внутри - болтун (Л), Трутни горазды на плутни (T)

Cf: By doing nothing we learn to do ill (Am., Br.). The devil finds work for idle hands (Am., Br.). The devil some mischief finds for idle hands to do (Am.). Idle hands are the devil's tools (Am.). An idle mind is the devil's workshop (Am., Br.). Idleness is the devil's workshop (the mother of all evil, the mother of sin, the mother of vice) (Br.). Idleness is the mother of evil (of mischief) (Am.). Idleness is the parent of many vices (Am.), Idleness is the parent of vice (Br.). Idleness is the root of all evil (Am., Br.). Satan finds mischief (work) for idle hands (Br.). Satan has some mischief /still/ for idle hands to do (Am.). Sloth is the mother of vice (Am.)