[Andreas]

1. Add the following phrase to phrasegroup Control Panel Stop Messages:
   varname=no_reason_given
   text=You must enter a reason why you are going to ban this user
   (Or any other text you would like to have as an error message if no reason is given)
2. In modcp/banning.php FIND
   
   PHP Code:

   // check that the target usergroup is valid 

   ABOVE that ADD
   
   PHP Code:

   if (!$banreason) {
  print_stop_message('no_reason_given');
}