How to check whether user has seen push notification prompt before in iOS?

I wanted to show a message to users at the start of the app just before showing the push notification prompt. In order to determine whether I should display the message, I need to know whether user has seen the push notification prompt before.

NOTE : First I assumed, if the app is launching for the first time, users haven't seen the prompt and I used NSUserDefaults to store an indication of the the first run. But if the app is deleted and installed within the same day, push notification prompt will not be shown, even if it is the first run.