The holy spirit in Islam is the Angel Gabriel (Peace be upon him)
Perhaps in Islam, but it is not possible to identify the Angel Gabriel with the Holy Spirit in Christianity. See this story:
Luke 1
26In the sixth month, God sent the angel Gabriel to Nazareth, a town in Galilee, 27to a virgin pledged to be married to a man named Joseph, a descendant of David. The virgin's name was Mary. 28The angel went to her and said, "Greetings, you who are highly favored! The Lord is with you."
29Mary was greatly troubled at his words and wondered what kind of greeting this might be. 30But the angel said to her, "Do not be afraid, Mary, you have found favor with God. 31You will be with child and give birth to a son, and you are to give him the name Jesus. 32He will be great and will be called the Son of the Most High. The Lord God will give him the throne of his father David, 33and he will reign over the house of Jacob forever; his kingdom will never end."
34"How will this be," Mary asked the angel, "since I am a virgin?"
35The angel answered, "The Holy Spirit will come upon you, and the power of the Most High will overshadow you. So the holy one to be born will be called the Son of God. 36Even Elizabeth your relative is going to have a child in her old age, and she who was said to be barren is in her sixth month. 37For nothing is impossible with God."
38"I am the Lord's servant," Mary answered. "May it be to me as you have said." Then the angel left her.
Now shortening the story up a bit to point out why they cannot be one and the same, note the following:
1) God sent the angel Gabriel to Nazareth, a town in Galilee, to a virgin [who's] name was Mary.
2) The angel said to her, "Mary, you have found favor with God. You will be with child and give birth to a son, and you are to give him the name Jesus."
3) Mary asked the angel, "How will this be, since I am a virgin?"
4) The angel answered, "The Holy Spirit will come upon you...so the holy one to be born will be called the Son of God."
Gabriel did not indicate that he would have anything to do with Mary becoming pregnant, but he did indicate the the Holy Spirit would. Thus we are talking about two different entitites.
There are many other reasons, but this should be sufficient to show that at least from a Christian understanding (which is what you need when reading the Christian scriptures) the Holy Spirit and Gabriel are not one and the same, even if they might be portrayed that way in the Qur'an.
The comforter that is prophesied in the Gospel of John can only be referring to prophet Muhammad (Peace be upon him)
This is hardly true.
First, the actual term is
parakletos which you have translated Comforter (no criticism of that translation), is Counselor in the Bible I generally use, and translated into various other terms in other Bibles, as there is no precise translation for it in English or any other language I know. Never have I seen any Bible translate it as Muhammad. But I don't read Arabic, maybe it is that there. You tell me:
16 وَسَوْفَ أَطْلُبُ مِنَ الآبِ أَنْ يُعْطِيَكُمْ مُعِيناً آخَرَ يَبْقَى مَعَكُمْ إِلَى الأَبَدِ،
17 وَهُوَ رُوحُ الْحَقِّ، الَّذِي لاَ يَقْدِرُ الْعَالَمُ أَنْ يَتَقَبَّلَهُ لأَنَّهُ لاَ يَرَاهُ وَلاَ يَعْرِفُهُ، وَأَمَّا أَنْتُمْ فَتَعْرِفُونَهُ لأَنَّهُ فِي وَسَطِكُمْ، وَسَيَكُونُ فِي دَاخِلِكُمْ.
Second, Muhammad does not do the things that the Comforter is said to do:
- to be with you forever
- he lives with you
- will be n you
As Jesus was speaking directly to the disciples, and Muhammad was not even yet alive, how could any of these be true of Muhammad?
Later Jesus adds some more information about this Counselor/Comforter/paracletos:
When the Counselor comes, whom I will send to you from the Father, the Spirit of truth who goes out from the Father, he will testify about me.
John 15:26
If we are to identify this Counselor/Comforter/paracletos with Muhammad, then it would mean that Muhammad was not sent by Allah, but by Jesus. It would also mean that Muhammad's job is to testify about Jesus. Yet, that does not seem to be the focus of Muhammad's life and mission, other than to deny those things that the Gospel of John records about Jesus.
So while Muslims love the verse in which Jesus says:
But I tell you the truth: It is for your good that I am going away. Unless I go away, the Counselor will not come to you; but if I go, I will send him to you.
John 16:7
They pick out only one small portion of it and say it points to Muhammad and dismiss everything else that Jesus told us was also true with regard to the Counselor. Things such as are included, not just in the above passages, but in Jesus continuation of his comments in this very passage:
John 16
7But I tell you the truth: It is for your good that I am going away. Unless I go away, the Counselor will not come to you; but if I go, I will send him to you. 8When he comes, he will convict the world of guilt in regard to sin and righteousness and judgment: 9in regard to sin, because men do not believe in me; 10in regard to righteousness, because I am going to the Father, where you can see me no longer; 11and in regard to judgment, because the prince of this world now stands condemned.
12"I have much more to say to you, more than you can now bear. 13But when he, the Spirit of truth, comes, he will guide you into all truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come. 14He will bring glory to me by taking from what is mine and making it known to you. 15All that belongs to the Father is mine. That is why I said the Spirit will take from what is mine and make it known to you.
Which of the above mentioned things are true of Muhammad?
- Muhammad coud not come unless Jesus went away.
- Muhammad convicted the world of guilt in regard to sin and righteousness and judgment.
- Muhammad would convict the world of sin because men do not believe in Jesus.
It is not enough for Muhammad to do some of these things, they must all be true of him, and all of the ones menitoned above in the other passages as well, if one is to consider that Muhammad is the one being referred to by Jesus when he speaks of the paracletos. If even one of these things is untrue of Muhammad, then he is not the one Jesus was speaking about. Simply put Muhammad does not qualify, for though some of these items might be interpreted to be true of him, the majority definitely are not.
And understand also this phrase "believe in" as John uses it. To "believe
in" is not to simply affirm that you believe something
about Jesus, but that one actually puts his/her trust in Jesus, that one depends on Jesus. To do so the way that John is speaking of would be for Muhammad to teach that Jesus could be depended on in the same way that Allah can; it would be to make Jesus a partner with Allah, to associate a human being with Allah. Surely Muhammad would never do such a thing. I am surprised Muslims even want to make the application.