How to hook add_action() into after category description with id?

Check this blog about adding something before the post content. Here is the code you need to add in functions.php:

add_filter('the_content', 'add_content_before');

function add_content_before($content) {

      $before_content = "Your pre-content to be here";

      $fullcontent = $before_content . $content ;

      return $fullcontent;

}