title: How to get invoice id from order increment id
body: <p>I have order increment id like 100000096 and i want to get its invoice id, please help me to achieve this in magento, i have tried with</p>
  
  <pre><code>                 $incrementId = '100000096';
                 $order = Mage::getModel('sales/order')-&gt;load($incrementId);
                     $invIncrementIDs = array();
                       foreach ($order-&gt;getInvoiceCollection() as $inv) {
                           $invIncrementIDs[] = $inv-&gt;getIncrementId();
                }
  </code></pre>
  
  <p>But it returns an empty array.</p>