User exit - sales order

Hi Gurus,

We need to have specific requirement while creating or changing a the sales order.

In the sale order if the line items are BOM material, then the system should ensure that confirmation of the qty between the BOM materials (both header and sub utems ) are same.

We wanted to achieve this with the help of a User Exit, which will look at the confirmation qty of each line item and then changes confirmation qty of all the line items if there exist a difference.

So wanted to which is the actual user exit which we can use to achieve above requirment.

Regards,

Babs