The only source for the life of jesus accepted by Christians is the Bible. Muslims believe Jesus to be a messenger of Allah the Almighty, as mentioned in the Quran.
They also accept the sayings of the Prophet as well as Biblical and historical narrations that tally with the Quranic narration about Jesus.
As for the Bible, it is the four Gospels in the New Testament that give the story of Jesus. Christians believe the Gospels to be divinely inspired writings by Jesus's own apostles, though there are strong evidences that establish the fact that the Gospel writers and Jesus's apostles were different persons.
It is generally believed that the Christians follow a religion founded by Jesus. But the Bible informs us that the name "Christians" was used first by outsiders, to refer to Paul and his followers in Antioch after Jesus's time:
"…..And the disciples were called Christians first at Antioch." (Acts 11:26, KJV)
This means that until this time, the Christian religion had been looked upon as a sect of Judaism, like the Pharisees and Sadducees. In other words, Jesus Christ actually did not found a religion called "Christianity".
It is usually taken for granted that Christianity is based on Jesus's teachings, but Jesus's teachings as given in the Gospels do not teach that Jesus was God or that his mission was to redeem those who accepted him from eternal damnation, by suffering and dying on the cross for their Original Sin.
Thus, the view about Christianity that all its tenets are derived from the words and deeds of Jesus Christ seems untenable.
For one thing, the Bible gives us a very meager account of Jesus's life and teachings. In fact, we are told nothing about his life from his birth to his thirtieth year, except for one incident in his twelfth year. (See Luke 2:42-46).
In other words, all the events in Jesus's mission as described in the Gospels, took place in about three years at the most.
The teachings of Jesus after allowance for duplication in the four Gospel accounts "could be printed in two columns of a newspaper".(Gary Miller, A Concise Reply to Christianity - A Muslim View) It is upon this foundation that the whole edifice of Christianity has been built. The missing Years
In Aristotelian philosophy, there is a theory that 'nature abhors a vacuum' and therefore, empty space would always be trying to suck in gas or liquids to avoid being empty. In Christian religious history too, we find a similar process of the vacuum in Jesus's life history absorbing fantastic theories and stories.
Jesus's years between twelve and thirty are left totally blank in the Gospels; and nothing is mentioned about his whereabouts or his activities during this time. These are the years commonly called his "missing years".
Now centuries after Jesus, we have several accounts of where Jesus was during these "missing years". One such account is given in the book called, "The Unknown Life of Jesus Christ" by the Russian writer Nicolas Notovitch.
Notovitch writes that during his travel to Tibet he found an amazing, ancient manuscript in a lamasery, which supplied him the material for his controversial book published in France in 1894.
In his foreword of the book "The Unknown Life of Jesus Christ", he wrote how he took advantage of a short stay in Ladakh among Buddhist monks to obtain the privilege of seeing the manuscripts relating to Christ. With the aid of an interpreter, he got them translated from the Tibetan tongue.
According to the story, Jesus visited Nepal and the Himalayan Mountains and thereafter went to "the valley of Rajputan and went westward, preaching to diverse people."
It is also said that Jesus was twenty nine years of age when he finally arrived back in Israel.
There are two other books about the life of Jesus in the East after the alleged crucifixion. The first one is, A Search for the Historical Jesus. From Apocryphal, Buddhist, Islamic & Sanskrit Sources written by Fida M. Hassnain (first published 1994 by Gateway Books, U.K.), the second one is Jesus Lived in India by Holger Kersten.
The second book is a thorough and methodical examination of the evidence of Christ's life beyond the Middle East before 'the Crucifixion' in India and elsewhere after it.
This is an exhaustive research into Christ's travels after 'the Crucifixion', his arrival in India with the Mother Mary and finally his death and entombment in Kashmir.
This is a summary of the two books:
For about sixteen years, Christ traveled through Turkey, Persia, Western Europe and possibly England. He finally arrived with Mary at a place near Kashmir, where she died. After many years in Kashmir, teaching to an appreciative population, who venerated him as a great prophet, reformer and saint, he died and was buried in a tomb in Kashmir itself.
If we examine the claims in all those books on Jesus' life in India against the background of the Gospels and the Judaic traditions that served as a background to the mission of Jesus, the following facts come to light:
The claims about Jesus' travel to India are exaggerated and their sources are unreliable. The alleged scrolls that Nicolas Notovitch claimed to have seen have never been produced and the monks who were supposed to possess them denied any knowledge of them. (Gregory Koukl, Jesus's Missing Years)
The Gospel accounts of Jesus betray a strong repugnance on the part of Jesus towards tolerating gentile culture steeped in idolatry, as he was brought up in Hebraic traditions.
And above all, the Gospels clearly teach that he stayed in Palestine; and there is no shred of evidence to show that he had at any time crossed its boundary.
With regard to the Muslims' take on this issue, the Quran has mentioned twenty five prophets by name; and has given in some cases details of the challenges they faced in the performance of the mission entrusted to them. For example, Noah, Abraham, Moses and Jesus (peace be upon them all).
In some other cases, we find only a very brief mention of their role as prophets. For example, Dhul Kifl, Ilyas and Al-Yasa (peace be upon them).
From the Islamic point of view, all prophets of Allah deserve equal respect from us, whether their life history is given in detail or not. And no prophet's life is narrated in detail to include events that happened in every year of their life either.
The Quran mentions only what Allah has deemed necessary to inform us, by way of teaching His guidance; and in the matter of the life of prophets, no systematic 'biography' of a prophet is given in a modern sense.
What is absolutely necessary for us to know from the Islamic point of view about Jesus' life and mission has been mentioned in the Quran and the Hadith; and the rest is irrelevant.
So in Islam, the question of any missing years does not arise in the case of any prophet, including Jesus of Nazareth.