You can use user_permission_get_modules() function, which returns an array of all defined permissions and their modules.
Determine the modules that permissions belong to.
###Return value
An associative array in the format $permission => $module.
A simple one-off method to inspect would be using drush. You could further grep to refine for a specific permission you're after or a specific module providing it:
drush ev "print_r( user_permission_get_modules() );" | grep -i my_custom
returns something like
[configure participant automator] => my_custom