how to block changing a quotation which is adopted by a purchase order?

Hi people,

I'm new to SAP and recently I was tasked to research on How to block changing a quotation which is being adopted by a purchase order. The process scenario should be:

- User goes to ME21N and create a purchase order that adopts a quotation.

- User goes to ME47 (maintain quotation) and enter the adopted quotation number

Expect: not allow user to change that adopted quotation.

I am working on an idea of using status profile, but everything is still hard to understand.

I would be very appreciated if anyone can help me with this (step by step would be very nice).

Thanks in advance.