In which paper is written that you can transform one problem to another to show NP-completeness?
If I may make an assumption, you want such a reference to be able to put it in one of your works, right ? I don't why you would wanna do that as if you have a problem A, reducting a NP Hard problem to problem A quite clearly shows that A is NP Hard. No one bothers proving it as it's such a straightforward and fundamental result. If you need to prove it for some reason you can do it in two lines. If you still want a reference for a reader to read about NP in general then just quote Arora and Barak's book on complexity theory.