Changing default password reset e-mail text

I would like to change the text in the default email that is sent to users who forgot their password. Currently, the auto-generated email begins with "Hi," followed by a user's first-name. We would like to be able to change the text in the e-mail that is sent out to say something completely different yet still have the link.

I see Site Administration-> Language-> Language Editing, but when I choose to "Edit words or phrases," I do not see forgot_password.php as an option in the drop-down.

Any suggestions to complete this change?

Thanks!