How to disable the dynamic sidebar on single posts?

<div id="sidebar-left">
<ul class="sidebar_list">
<?php if (!function_exists('dynamic_sidebar') || !dynamic_sidebar(3)) : ?>

<li class="widget_categories">
<h6>Categories</h6>
	<ul>
	<?php wp_list_categories('orderby=name&show_count=1&use_desc_for_title=0&title_li=&depth=1'); ?>
	</ul>
</li>

<li class="widget_pages">
<h6>Pages</h6>
	<ul>
	<?php wp_list_pages('orderby=name&title_li=&depth=1'); ?>
	</ul>
</li>

<li class="widget_archive">
<h6>Archives</h6>
	<ul>
	<?php wp_get_archives('type=monthly&limit=12&show_post_count=1'); ?>
	</ul>
</li>

<?php endif; ?>
</ul><!-- SIDEBARLIST END -->
</div><!-- SIDEBAR LEFT END -->