Try this;
$('.modal-edit').on('click', function () {
// create the backdrop and wait for next modal to be triggered
$('body').modalmanager('loading');
var edit = $(this).attr("data-id");
setTimeout(function () {
$modal.on('show', function () {
$('iframe').attr("src", 'Customer_User.aspx?edit=' + edit + '');
});
$modal.modal()
//$modal.load('Customer_User.aspx?edit=' + edit + '', '', function () {
// $modal.modal();
//});
}, 100);
});
<div id="ajax-modal" class="modal fade" tabindex="-1" data-width="760" >
<iframe ></iframe>
</div>