I think Muslims imagine that "the Prophet" is Muhammed; and (if I remember right) that the Comforter is also Muhammed! They teach that the Bible was drastically altered by Christians, although there's no historical evidence for it of course.
Is your friend genuinely interested in what the Bible says or is he just repeating what he's been taught about it? Has he even read a good translation of the Quran, let alone the Bible? Apparently many Muslims haven't, partly because its traditionally supposed to only be read in the original Arabic. Rather like the old Catholic tradition of having services in Latin.
It might be a good idea to get a book on what Islam teaches. A good one, from the point of view of a former Muslim scholar (he was a lecturer in the top Muslim university in Egypt) is "Jesus and Muhammad" by Mark A Gabriel.
The question I would like to ask a Muslim would be concerning the personalities of Jesus and Muhammed. Judging merely by what the [i]Quran[/i] says about both of them which of the two would they most like to have as a personal friend? Should set him thinking!
Also why, if Muhammed is supposed to be greater than Jesus, [i]the Quran[/i] says Jesus did lots of miracles when Muhammed didn't.
They do respect Jesus as a prophet, just don't see Him as THE prophet, and of course the phrase "son of God" is horrible to them as they think it means God had sex with Mary.
Praying that your friend will find the true God
Jeannette