BundleConfig.cs

bundles.UseCdn = true;
BundleTable.EnableOptimizations = true;

var jquery = new ScriptBundle("~/bundles/jquery", "//ajax.aspnetcdn.com/ajax/jquery/jquery-1.9.1.min.js")
    .Include("~/Scripts/jquery-{version}.js");
jquery.CdnFallbackExpression = "window.jQuery";
bundles.Add(jquery);

output.html

<script src="//ajax.aspnetcdn.com/ajax/jquery/jquery-1.9.1.min.js"></script>
<script>(window.jQuery)||document.write('<script src="/bundles/jquery"><\/script>');</script>