Yes Olivnt, you are correct. The Don asks Hagen, on page 71 of the novel " What time do I have to meet this infidel tomorrow"

I know that the term Infidel is used mostly in religious references. However, in reading that verse and paragraph in the novel, I don't think that Vito meant it as a religious reference. That may be your interpretation, but my interpretation is that Vito called him this because Vito did not believe in dealing with drugs, and therefore referred to Sollozzo in that manner becasue Vito knew that Sollozo did not Believe in or share the same morals that he ( Vito) did in regards to the drug trade. For some reason I do not think that Vito would refer to and judge the man on his religious beliefs, but instead would judge the man on his beliefs in the area of mob business itself.

Don Cardi