I believe God is one Lord (Mark 12:29). He manifests himself in the form of the Father, the Word (the Son) and the Holy Ghost; but these three are one (1 John 5:7).
Refs:
Mark 12:29-30 "...The first of all the commandments is, Hear, O Israel; The Lord our God is one Lord: And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength: this is the first commandment."
1 John 5:7 "For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one."
Jesus also said, "I and my Father are one" (John 10:30); and it is written: "the Word was made flesh, and dwelt among us..." (John 1:14); that is, the Word and Jesus are also one.
Um, I am not muslim.
I am just noting the muslim position regarding Christianity. This position, like most all of their "religion" is stupid.
But it is their position, and important to know --- otherwise, Izamadajihadi's call for "monotheism" sounds OK.
Not all Christians are Trinitarians.