Classic book by MarshallMcLuhan (ISBN 1584230703 )
You can have a look, for example, at M.Mcluhan's "Understanding Media" whose Chapter 1 (Part I) is called "The Medium is the Message".
To clarify: McLuhan said "The medium is the message". He later wrote TheMediumIsTheMassage, intentionally making that title a little bit of a joke.
Thus neither is an incorrect quote, they are both correct quotes, the original version was "message", and McLuhan's joke version is "massage".
The Medium Is The Massage is also a gramophone record (I happen to possess a copy).
http://www.marshallmcluhan.com/faqs.html