Source

File: wp-includes/comment-template.php

function get_comment_author_url( $comment_ID = 0 ) {
	$comment = get_comment( $comment_ID );
	$url     = '';
	$id      = 0;

	if ( ! empty( $comment ) ) {
		$author_url = ( 'http://' === $comment->comment_author_url ) ? '' : $comment->comment_author_url;
		$url        = esc_url( $author_url, array( 'http', 'https' ) );
		$id         = $comment->comment_ID;
	}

	/**
	 * Filters the comment author's URL.
	 *
	 * @since 1.5.0
	 * @since 4.1.0 The `$comment_ID` and `$comment` parameters were added.
	 *
	 * @param string     $url        The comment author's URL.
	 * @param int        $comment_ID The comment ID.
	 * @param WP_Comment $comment    The comment object.
	 */
	return apply_filters( 'get_comment_author_url', $url, $id, $comment );
}