function add_rewrite_rules( $wp_rewrite )
{
    $new_rules = array(
        'thoughts/(.+?)/?$' => 'index.php?post_type=post&name='. $wp_rewrite->preg_index(1),
    );

    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'add_rewrite_rules'); 

function change_blog_links($post_link, $id=0){

 $post = get_post( $id );
  if( is_object( $post ) && $post->post_type == 'post' ) {
    return home_url( '/thoughts/' . $post->post_name );
  }
  return $post_link;
}
add_filter('post_link', 'change_blog_links', 1, 3);