Redirecting with apache mod_rewrite

How do I redirect
http://hostname.com/about
to
http://hostname.com/foo/index.php/pages/about
with apache mod_rewrite, without changing url in browser?

I tried writing this:
but displays the "404 Page Not Found" page from CodeIgniter (not the Apache default one).

This works:
But it changes url in the browser, which is not what I needed.

I think the problem might be in the query string part, but can't figure out a way to solve it yet.