An IM told me once : You can't learn the Najdorf by reading books . You may read theory or general guidance but don't expect to understand the opening with out play countless games before and gain your own experience on it.
I have three books in the Najdorf. I suggest none.
This is one of the best books written on the Najdorf, but it only covers 6.Bg5. The size of this book and the fact that it only covers one of about seven options for White ought to give you the picture of what you are getting yourself into if you try to take up the Najdorf!
https://www.amazon.com/Chess-Developments-Sicilian-Najdorf-Bg5/dp/1781940215/ref=sr_1_1?s=books&ie=UTF8&qid=1495201389&sr=1-1&keywords=Chess+Developments+Najdorf
I have thought av bit about learning the najdorf but I have no experience with it at all. I am about 2050 elo. Which books would you recommend to learn the najdorf from scratch?