The 1963 film Saladin is said to be based on a novel. Which one?

Question

I am researching the 1963 film Saladin, directed by Youssef Chahine for my MA Thesis. I have read a number of places that it is based upon a novel written by Naguib Mahfouz, the famous Egyptian writer. However, I cannot for the life of me figure out which one it was.

Answer 1

Original Literary Source
Mahfouz, Naguib. Naser Salah el Dine, El

http://imdb.com/title/tt0057357/literature