Think about it.
You're saying that you want to ask people if they want you to save the passwords they have set up to access something on your site. Why would you want to do that? You must save the passwords, otherwise how will your site know when someone enters one correctly?
User passwords are saved in a database, and your site uses an authentication protocol to check an entered password against the list on the server. Users can't say 'no, I don't want my password saved' can they?