What Do Muslims Think about the Gospels?
Question

It is well known among us Muslims that Allah revealed the Gospel (Injil) to `Isa (peace and blessings of Allah be upon him), but when I studied some things about Christianity, they told me that the Gospel was not brought by the Messiah, rather it was written by the disciples of the Messiah after the crucifixion (or after Allah raised him up to Him, as it says in the Quran). How can we reconcile between the two views?
Praise be to Allah.There is no contradiction between the two views such that we would need to ask how they can be reconciled. Rather the reason why the questioner is confused is that he is mixing up two things that we must believe in and that are both true, praise be to Allah. 
What Do Muslims Think about the Gospels?
The first issue is to believe that Allah, the Lord of the Worlds, revealed a Book to His Prophet `Isa (peace and blessings of Allah be upon him) and that the name of this book was the Gospel (Injil) . These are basic principles of faith that we must believe in. Allah says (interpretation of the meaning): 
“The Messenger (Muhammad) believes in what has been sent down to him from his Lord, and (so do) the believers. Each one believes in Allah, His Angels, His Books , and His Messengers. (They say,) `We make no distinction between one another of His Messengers’ — and they say, `We hear, and we obey. (We seek) Your forgiveness, our Lord, and to You is the return (of all)’.” [Al-Baqarah 2:285]
The Prophet (peace and blessings of Allah be upon him) said to Jibril (peace be upon him), when he asked him about faith, as mentioned in the well-known Hadith: “Faith means to believe in Allah, His angels, His books, His messengers, the Last Day, and to believe in His divine will and decree, both good and bad.” (Al-Bukhari and Muslim) 
Disbelieving in that or doubting it is misguidance and disbelief in Allah
Allah says (interpretation of the meaning): 
“O you who believe! Believe in Allah, and His Messenger (Muhammad), and the Book (the Quran) which He has sent down to His Messenger, and the Scripture which He sent down to those before (him); and whosoever disbelieves in Allah, His Angels, His Books, His Messengers, and the Last Day, then indeed he has strayed far away. Verily, those who believe, then disbelieve, then believe (again), and (again) disbelieve, and go on increasing in disbelief; Allah will not forgive them, nor guide them on the (right) way.” [An-Nisa’ 4:136-137] 
“Verily, those who disbelieve in Allah and His Messengers and wish to make distinction between Allah and His Messengers (by believing in Allah and disbelieving in His Messengers) saying, “We believe in some but reject others,” and wish to adopt a way in between. They are in truth disbelievers. And We have prepared for the disbelievers a humiliating torment.” [An-Nisa’ 4:150-151]
Does the original Gospel exist today?
The second issue is the Gospel or, more precisely, the Gospels that the Christians have today. Although one of the basic principles of our faith is to believe in the Gospel that was revealed to `Isa (peace and blessings of Allah be upon him), we also believe that, apart from the Quran, no book remained as it was revealed by Allah, neither the Gospel nor anything else . Even the Christians themselves do not believe that the books which they have were revealed in that form from Allah, nor do they claim that the Messiah wrote the Gospel, or at least that it was written during his lifetime. 
Imam Ibn Hazm (may Allah have mercy on him) says in Al-Fasl Fil-Milal (2/2): 
“We do not need to try hard to prove that the Gospels and all the books of the Christians did not come from Allah or from the Messiah (peace be upon him), as we needed to do with regard to the Torah and the books attributed to the Prophets that the Jews have, because the Jews claim that the Torah that they have was revealed from Allah to Moosa, so we needed to establish proof that this claim of theirs is false. 
With regard to the Christians, they have taken care of the issue themselves, because they do not believe that the Gospels were revealed from Allah to the Messiah, or that the Messiah brought them, rather all of them from first to last, peasants and kings, Nestorians, Jacobites, Maronites and Orthodox are all agreed that there are four historical accounts written by four known men at different times. 

The first of them is the account written by Matthew the Levite who was a disciple of the Messiah. He wrote it nine years after the Messiah was taken up into heaven. He wrote it in Hebrew in Judaea in Palestine, and it filled approximately twenty-eight pages in a medium-sized script. 
The next account was written by Mark, a disciple of Simon ben Yuna, who was called Peter. He wrote it twenty-two years after the Messiah was taken up into heaven. He wrote it in Greek in Antioch in the land of the Byzantines. They say that Simon is the one who wrote it, then he erased his name from the beginning of it and attributed it to his disciple Mark. It filled twenty-four pages written in a medium-sized script. Simon was a disciple of the Messiah. 
The third account written was that of Luke, a physician of Antioch who was also a disciple of Simon Peter. He wrote it in Greek after Mark had written his account, and is similar in length to the Gospel of Matthew. 
The fourth account was written by John the son of Zebedee, another disciple of the Messiah, sixty-odd years after the Messiah had been taken up into heaven. He wrote it in Greek, and it filled twenty-four pages in a medium-sized script.”

Who wrote the Gospels and when were they written?
Shaykh Al-Islam Ibn Taymyiyah (may Allah have mercy on him) said in Al-Jawab As-Sahih (3:21): 
“With regard to the Gospels that the Christians have, there are four Gospels, Matthew, Mark, Luke and John. They agree that Luke and Mark did not see the Messiah; instead, he was seen by Matthew and John. These four accounts which they call the Gospel, and they call each one of them a Gospel, were written by these men after the Messiah had been taken up into heaven. They did not say that they are the word of Allah or that the Messiah conveyed them from Allah, rather they narrated some of the words of the Messiah and some of his deeds and miracles.”
Moreover, these books which were written after the time of the Messiah did not remain in their original form. The original versions were lost long ago. 
Ibn Hazm (may Allah have mercy on him) said:
“With regard to the Christians, there is no dispute among them, or anyone else, that only one hundred and twenty men believed in the Messiah during his lifetime… and all of those who believed in him concealed themselves and were afraid during his lifetime and afterwards. They called people to his religion in secret and none of them disclosed himself or practised his religion openly, because any of them who was caught was executed. 
They continued in this manner, not showing themselves at all, and they had no place where they were safe for three hundred years after the Messiah was taken up into heaven . 
During this time, the Gospel that had been revealed from Allah disappeared, apart from a few verses which Allah preserved as proof against them and as a rebuke to them, as we have mentioned. Then when the Emperor Constantine became a Christian, then the Christians prevailed and started to practise their religion openly and assemble in safety. 
If a religion is like this, with its followers practising it in secret and living in constant fear of the sword, it is impossible for things to be transmitted soundly via a continuous chain of narrators, and its followers cannot protect it or prevent it from being distorted .” (Al-Fasl, 2/4-5) 
In addition to this huge disruption in the chain of transmission of their books, which lasted for two centuries, these books did not remain in the languages in which they were originally written, rather they were translated, more than once, by people whose level of knowledge and honesty is unknown. The contradictions in these books and their shortcomings are among the strongest evidence that they have been distorted and that they are not the Gospel (Injil) that Allah revealed to His slave and Messenger `Isa (peace and blessings of Allah be upon him). Allah indeed spoke the truth when He said (interpretation of the meaning): 
“Had it been from other than Allah, they would surely have found therein many contradictions.” [An-Nisa’ 4:82].
And Allah knows best.