Its simply question, when i trying to make validation method on laravel, i can use like

$rules = [
  'username' => 'required,unique:Userlogin,username',
  'password' => 'required',
  'email'    => 'required,unique:Userlogin,email'
];

$messages = [
  'required'  => 'The :attribute field is required.',
  'unique'    => ':attribute is already used'
];

$request->validate($rules,$messages);

But how can i make custom error message on laravel precognition?