WordPress: Releted posts by tags

functions.php

/*
* List the related posts by current post tags.
*/
function m3_related_posts(){
	$tags = wp_get_post_tags($post->ID);
	if ($tags) {
	  echo 'Related Posts';
	  $first_tag = $tags[0]->term_id;
	  $args=array(
	    'tag__in' => array($first_tag),
	    'post__not_in' => array($post->ID),
	    'no_found_rows' => 1, 
	    'post_status' => 'publish',
	    'posts_per_page' => 5
	   );
	  $related_posts = new WP_Query($args);
	  if( $related_posts->have_posts() ) {
	    while ($related_posts->have_posts()) : $related_posts->the_post();
		echo '<div class="post m3-posts">';
		if  ( has_post_thumbnail() ){
			printf('<a href="%s" title="%s" rel="bookmark" class="post-thumbnail alignleft">%s</a>', get_permalink(), the_title_attribute( 'echo=0' ), get_the_title() );
		}
		printf('<h2><a href="%s">%s</a></h2><p class="byline post-info"><span class="date published time">%s</span></p>', get_permalink(), get_the_title(), get_the_time(get_option('date_format')));
		echo '</div><!--end m3-posts -->';
	    endwhile;
	  }
	}
	wp_reset_query();
}