Link to a heading by number in ReST

I have a ReST (ReStructured Text) document that auto-numbers headings 
like:

    My Heading
    ----------

which will be given a number like 10.1 (say), except of course I don't 
know what the number will be until I've compiled the .rst file.

I'm using this as a legal document, where the canonical way to refer to 
a clause is by number, not title. So rather than say:

    see clause My Heading ...

I want to say 

    see clause 10.1 ...


How can I do this using ReST and/or Sphinx?



-- 
Steve

------------------------------------------------------------------------------