Make use of the get_comment_link
function in your foreach
loop like so:
foreach ($comments as $comment) {
$output .= '<li><strong>'
. $comment->comment_author
. ' said</strong> : "'
. '<a href="'
. get_comment_link( $comment->comment_post_ID )
. '">'
. strip_tags($comment->com_excerpt)
. '..."</a></li>';
}