Mian_Haseeb on "wp-admin's folder index.php file replaced itself"

Hi
My WordPress dashboard is not opening. When I go here abc.com/wp-admin , it is showing this error.

Warning: include(./wp-admin/includes/class-wp-admin-list-table.php): failed to open stream: No such file or directory in /home/lilypark/public_html/oran-park.com.au/wp-admin/index.php on line 8

Warning: include(): Failed opening './wp-admin/includes/class-wp-admin-list-table.php' for inclusion (include_path='.:/usr/local/lib/php') in /home/lilypark/public_html/oran-park.com.au/wp-admin/index.php on line 8

Warning: require(/home/lilypark/public_html/oran-park.com.au/wp-admin/wp-blog-header.php): failed to open stream: No such file or directory in /home/lilypark/public_html/oran-park.com.au/wp-admin/index.php on line 17

Fatal error: require(): Failed opening required '/home/lilypark/public_html/oran-park.com.au/wp-admin/wp-blog-header.php' (include_path='.:/usr/local/lib/php') in /home/lilypark/public_html/oran-park.com.au/wp-admin/index.php on line 17

When i replace index.php file in wp-admin folder with new index.php file, then my dashboard work goods.

But

After few days my all websites encounter same problem again. After replacing index file it works fine but this is happening again and again after somedays to all my websites.

This is the code which infected index.php file contains

<?php
/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */
include "./wp-admin/includes/class-wp-admin-list-table.php";
/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool
 */
define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
require( dirname( __FILE__ ) . '/wp-blog-header.php' );

I am using Godaddy hosting, they said there is no issue on their end. Please help me to resolve with this issue.

Thanks