Page Load fires twice on every first time pageload using updatepanel

Thanks for giving reply @dharmendr

<script type="text/javascript">
    $(document).ready(function () {
        Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded(function () {
            ToDatePicker();
        });

        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
        function EndRequestHandler(sender, args) {
            ToDatePicker();
        }
    });

    function ToDatePicker() {
        $('#<%=TxtTo.ClientID%>').datepicker({
            changeMonth: true,
            changeYear: true,
            yearRange: '-5:+0',
            duration: 'fast',           
            dateFormat: 'dd-M-yy',
            showAnim: 'slideDown',
            maxDate: '0'
        });

    }
</script>

above script code solved the my problem. Thanks all