static member in a class when having forward declared members

Question

Let say I have class foo which has a member bar forward declared in it. If I want to use a static function in the class do I need to know the definition of bar?

class bar;
class foo:
{
   private:
   bar m_bar;
   
   public:
   static int DoStuff();
}

If I use foo::DoStuff(); by including foo.h do I need to know anything about bar?