2nd snippet in post "How to Check Whether Other WordPress Plugin is Active or Not"

gistfile1.phtml

function prfx_admin_notice() {
	ob_start();
	?>
	<div class="error">
		<p><?php _e( 'Easy Digital Downloads plugin is required to activate EDD sales number extension plugin. Please install and activate it first.' ); ?></p>
	</div>
	<?php
	echo ob_get_clean();
}