Try adding a RewriteCond (Rewrite Condition) before the RewriteRule. I would try writing something like this:

RewriteCond %{REQUEST_URI} !^.*(abc).*$ [NC]

Here is some additional reading if this doesn't help:
- http://www.whoopis.com/howtos/apache-rewrite.html
- http://www.sitepoint.com/article/apache-mod_rewrite-examples/

Correct way in new versions of nginx

Turn out my first answer to this question was correct at certain time, but it turned into another pitfall - to stay up to date please check Taxing rewrite pitfalls

I have been corrected by many SE users, so the credit goes to them, but more importantly, here is the correct code:

server {
       listen         80;
       server_name    my.domain.com;
       return         301 https://$server_name$request_uri;
}

server {
       listen         443 ssl;
       server_name    my.domain.com;
       # add Strict-Transport-Security to prevent man in the middle attacks
       add_header Strict-Transport-Security "max-age=31536000" always; 

       [....]
}