How to Register these class In Autofac

I am using autofac as Ioc Container. I have Three Classes:

class Service
{
     public Service(Repository rep,UnitOfWork context){}

}

Class Repository
{
     public Repository(UnitOfWork context){}
}

class UnitOfWork{}

the Service and Repository need the same instance of UnitOfWork

How to do that? and How to wirte it in XmlConfiguration