Unable to load the requested file

I tried to create a login system using ion_auth library
 This is my welcome controller:

PHP Code:

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Welcome extends CI_Controller {

public function __construct(){
    
parent::__construct();
$this->load->library('ion_auth');
  if (!$this->ion_auth->logged_in())
    {
    redirect('auth/login', 'refresh');
     
    }
    
}

    public function index()
    {
    $this->load->view('welcome_message');


    }
} 


 When I Run this shows an error

An Error Was Encountered

Unable to load the requested file: auth/login.php

How can I fix this?