ABSPATH not working! Any idea why?

This is what in my wp-config.php :

if ( !defined('ABSPATH') )
    define('ABSPATH', dirname(__FILE__) . "https://wordpress.stackexchange.com/");

I am calling from plugin/pluginName directory to :

require_once( ABSPATH . 'wp-includes/user.php');

But it is returning:

Warning: require_once(ABSPATHwp-includes/user.php) [function.require-once]: failed to open stream: No such file or directory in /home/------/wp-content/plugins/---/---.php on line 43

Fatal error: require_once() [function.require]: Failed opening required 'ABSPATHwp-includes/user.php' (include_path=".:/usr/lib/php:/usr/local/lib/php") in /home/------/wp-content/plugins/---/---.php on line 43

Any idea why I am having this error? Any solution?
Thanks.

If you just need that class included, and your script is located in the plugin directory, like /wp-content/plugins/pluginName/script.php, then you can do:

require realpath('../../../wp-includes/class-phpass.php');