Need a formula to place todays date in cell when other cell ="closed"

I think the title pretty much describes it.. Basically in one column I have the status. Once the status in cell A2 is set to closed, then I want another corresponding cell, in my example B2 to display todays date. However, I want that date to be permanent. In other words I don't want it to continually update day after day. I just want it to put in the date that Closed is selected from cell A2.

Let me know you have any more questions! Hopefully its not too confusing..

I fiddled around with a formula in my example sheet but it didn't work..

Thanks for the help!