Is possible to maintain linked estimate with invoice after create invoice ?

Could you explain what you are wanting when you say, linked estimate?

Since an invoice is a final sale, why?  But the estimate would show under the customer transaction listing

because if my client call by the estimate number  there is no way I can verify that estimate has already an invoice .

Hi spacetoursbus538,

You'll want to convert an estimate into an invoice first to generate an invoice number. Once done, open the estimate to enter the invoice in question under the Message displayed on estimate box.

Here's how:

1. Click Sales on the left panel.
2. Go to the All Sales tab, select the Estimate.
3. On the Message displayed on estimate box, enter the invoice no. (This will also show once the form is emailed)
   
4. Click Save and close.

Then, you can add a custom field for the estimated number in your invoice. Here's how:

1. Click the Gear icon.
2. Select Account and Settings.
3. Go to the Sales tab on the left panel.
4. Under Sales form content, click the pencil icon on the right side. 
5. Tick the box and add Estimate No. under Custom fields.
   
6. Click Save and Done.

Once you open the estimate form, you can enter the number of the custom field for reference. I've attached a screenshot for your visual guide.

Here's an article for more information about invoice customization: How to Customize Invoices in QuickBooks Online.

Keep me posted if you need anything else. I'm always right here to help.