Quotation reference in sales order for query report

I want to set up a query report that shows me the days passed between a submitted quotation and a corresponding sales order, but I do not know how to get both documents linked. Any ideas? Do I need to add a reference field that is being auto-populated when creating the sales order out of the quotation or is it possible to create the report with what i got?

Thanks in advance.

Solution: there is a quotation reference within the Sales Order Item Child Table.