This one?
do_action( 'register_post', $sanitized_user_login, $user_email, $errors );
http://phpxref.ftwr.co.uk/wordpress/nav.html?wp-login.php.source.html line 316
This one?
do_action( 'register_post', $sanitized_user_login, $user_email, $errors );
http://phpxref.ftwr.co.uk/wordpress/nav.html?wp-login.php.source.html line 316