Customize AJAX Calendar to Handle Hijri Date

I use the AJAX Calendar to Extend many textboxs in my application it uses Gregorian Date by default, while I use Hijri date in my application I used the culture = "ar-SA" in the page tag to use Hijri date Calendar show the Hijri calendar with no problems but , if I select any date it selects another date I need you to cusotmize it to handle hijri date than I can use it any where in the application