The Muslims are all obliged to believe in the Gospel (Injil) that Allah revealed to His Prophet Jesus the Messiah (peace be upon him). The one who denies this is a kafir (disbeliever) according to scholarly consensus.
Allah says (interpretation of the meaning):
“And in their footsteps, We sent ‘Isa, son of Maryam, confirming the Tawrat that had come before him, and We gave him the Injil, in which was guidance and light and confirmation of the Tawrat that had come before it, a guidance and an admonition for Al-Muttaqoon (the pious).” [5:46]
Our belief in the Gospel dictates that we should also believe that it exists and that it was revealed completely, and we believe that everything that he brought from Allah was true.
But there is nothing in Islam to tell us whether this Gospel was written and compiled at the time of ‘Isa (peace be upon him) or who wrote it, or who preserved it and disseminated it, or whether the Messiah taught it to the people orally or whether the disciples transmitted it and who believed in it, or whether some of it was written down and some was not. These are questions that we cannot answer for certain nowadays, rather some researchers deny that there was even a true Gospel that was compiled in the form of a book; rather it was just words that were transmitted.
The great scholar al-Tahir ibn ‘Ashoor says in al-Tahreer wa’l-Tanweer, commenting on the tafsir of Surat Al ‘Imran:
With regard to the Gospel, this is the name of the revelation that was sent to ‘Isa (peace be upon him) and was compiled by his companions. End quote.
Shaykh Ahmad Deedat (may Allah have mercy on him) said:
We believe sincerely that everything that ‘Isa (peace be upon him) said was revelation from Allah, and that it was the Gospel and glad tidings for the Children of Israel. But throughout his life, ‘Isa did not write a single word, and he did not order anyone to write anything. Hal al-Kitab al-Muqaddas Kalimat Allah (Is the Bible God’s Word?).
But it seems that the Messiah (peace be upon him) knew how to read and write. This may be understood from the words of Allah (interpretation of the meaning):
“And He (Allah) will teach him [‘Isa] the Book and Al-Hikmah (i.e. the sunnah, the faultless speech of the Prophets, wisdom), (and) the Tawrat and the Injil.” [Al ‘Imran 3:48]
Ibn Kathir (may Allah have mercy on him) said:
It seems that what is meant by Book here is writing. Tafsir al-Quran il-‘Azeem.
But we do not have any evidence that the revelation was written down at the time of ‘Isa (peace be upon him). The fact that the Gospel is called “a Book” in the Holy Quran does not indicate that it was written down on pages at the time it was revealed. The fact that it is called a Book only refers to that which is with Allah in al-Lawh al-Mahfooz (the Preserved Tablet), or that it was something that could be written. This also applies to the Holy Quran, as Allah calls it a Book. Rather it was transmitted verbally as well as being written down randomly on skins and parchments. In fact it was not a compiled Book until the time of Abu Bakr al-Siddeeq (may Allah be pleased with him). Indeed, Allah says (interpretation of the meaning):
“And even if We had sent down unto you (O Muhammad (peace and blessings of Allah be upon him)) a message written on paper so that they could touch it with their hands, the disbelievers would have said: ‘This is nothing but obvious magic!’” [6:7]
al-Tahir ibn ‘Ashoor said in his commentary on Surat Maryam:: 30:
The Scripture refers to the law which is usually written lest it be subject to change. The word Scripture is applied to the Law of ‘Isa (peace be upon him) just as it is applied to the Quran. Al-Tahreer wa’l-Tanweer.
Similarly the Christians do not believe that there is a book that was written by the Messiah or one of his disciples during his lifetime that was lost after that.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
As for the Gospel that is in their hands, they acknowledge that it was not written by the Messiah (peace be upon him), nor did he dictate it to someone else to write it down. Rather they wrote it after the Messiah was taken up (into heaven). Al-Jawab al-Saheeh.
There is a clear difference between the revelation that was sent down to Musa (peace be upon him) and the revelation that was sent down to ‘Isa (peace be upon him). In the Quran there is an indication that the former was written down, as Allah says (interpretation of the meaning):
“And We wrote for him on the Tablets the lesson to be drawn from all things and the explanation for all things (and said): Hold unto these with firmness, and enjoin your people to take the better therein. I shall show you the home of Al-Fasiqoon (the rebellious, disobedient to Allah).” [7:145]
Although it seems from the words of some Muslim scholars that the true Gospel was compiled and written at the time of the Messiah (peace be upon him). You can find this view in the words of Ibn Hazm in al-Fisal and Ibn Taymiyah in al-Jawab al-Saheeh.
Similarly it says that the word Gospel (Injil) is applied to that which Allah revealed to the Messiah, as it says in the Gospel of Mark 8:35: “… whoever loses his life for me and for the Gospel will save it”.
As for the Gospels that are extant nowadays, they are not the true Gospel, but no one can deny that they contain a great deal of the Gospel that Allah revealed to the Messiah (peace be upon him).
Ibn Taymiyah (may Allah have mercy on him) said:
These four books that they call the Gospel, or call each of them a Gospel, were written by them after the Messiah was taken up into heaven, but they do not say in them that they are the word of God, or that the Messiah conveyed them from God. Rather they transmitted in them some of the words of the Messiah, and some of his actions and miracles. They said that they did not narrate from him everything that they heard and saw from him. So they are more akin to what was narrated by the scholars of hadeeth (prophetic narrations), biography and maghaazi (battle) reports from the Prophet (peace and blessings of Allah be upon him) of his words and deeds that are not Quran. So the Gospels that they have in their hands are more like the books of seerah (biographies) and hadeeth (prophetic narrations), or like these books, even if most of them are true. Al-Jawab al-Saheeh.
And Allah knows best.