MAINLY ORAL TRANSMISSION OF THE QURAN FOR 43 YEARS
The revelations Muhammad (p.b.u.h.) received were passed on mainly orally for 43 years from 610 AD until 653 AD. At that time the Quran was officially written under the command of Uthman. During the first 22 years of this period the prophet of Islam was still alive. In case of doubt his followers could have consulted him immediately. Many of them also memorized the revelations under his personal guidance. More than 20 of those are mentioned by name in the Hadith. Among them were well know persons, such as Abu Bakr, Umar, Uthman, Ali, Ibn Masud, Abu Huraira, Abdullah bin Abbas, Abdullah bin Amr bin al-As, Aisha, Hafsa and Umm Salama. ("Itqan" by Suyuti, I, p.124) Others went over the contents of the Quran with the prophet before his death. "Narrated Qatada: I asked Anas bin Malik: 'Who collected the Quran at the time of the prophet?' He replied, 'Four, all of whom were from the Ansar: Ubai bin Ka'b, Muadh bin Jabal, Zaid bin Thabit and Abu Zaid.'" (Bukhari, VI, No.525)After the prophet's death they could be consulted and correct each other if there was any dispute that arose. Besides that, the tradition of memorizing the Quran has continued for many centuries throughout all generations until today.
In any case, secular history makes it clear that Islam spread within its first 25 years of the Hejira (the departure of Muhammad, p.b.u.h. from Mekkah) into many other countries outside Arabia. Damascus and Syria were taken in 13 AH. One year later Muslim armies made inroads into Persia. In 19 AH Egypt fell into Muslim hands. By 25 AH Islamic warfare brought success in Armenia, in northern Turkey. A lot of soldiers and leaders who conquered those far away countries had memorized at least parts of the Quran. They also knew about the historical events with regard to its beginnings. Within a short period of time the revelations Muhammad (p.b.u.h.) received spread in this way from Egypt to Persia and from Turkey to Arabia. Any changes within the Quran would surely have met with fierce opposition from all these parts of the world.
MAINLY ORAL TRANSMISSION FOR OF THE INJIL FOR 29-44 YEARS
The gospel was mainly passed on by oral means for 29 years from 26 AD until 55 AD when it's main teaching was first written down by Paul. This document, or book, is known as "1 Corinthians". (1 Cor. 15, verses 1-8, compare with Jesus' teaching in Matthew 26, verse 27 and Mark 14, verses 61-62 ) Its date is undisputed by all Biblical scholars. "1 Corinthians" is one of 27 parts that together form the New Testament. W.F. Albright, one of the world's best Biblical archaeologists, said: "We can already say emphatically that there is no longer any solid basis for dating any book of the New Testament after about 80 Ad." ("Recent Discoveries in Bible Lands" by Albright, 1955, p.136) Another renowned scholar summarizes that the whole New Testament was written before the Fall of Jerusalem in 70 AD. ("Redating the New Testament" by Robinson, 1976). It is very interesting that those scholars who would disagree with the above conclusions studied the matter on the basis of theories known as "documentary hypothesis" and "form criticism". They both deny vehemently that the Gospel was revealed by God, and that miracles and prophecies can be possible. This is the reason why true Muslims and Christians alike, have to reject their views, also regarding many of the alleged contradictions found in the Bible. Sadly speaking these liberal scholars are mostly referred to by Muslim authors and speakers.However, all scholars are in agreement that many of the New Testament books were written between 55 and 70 AD. In the light of this evidence the dates of 55 to 70 AD are taken as an average time period wherein the whole New Testament was officially written down. This allows for the balanced conclusion that the Gospel was transmitted predominantly by oral means for a period of 29-44 years.
During the first three years of this time Jesus was still with his followers. In case of doubt they could have consulted him. Afterwards, many of his disciples who memorized what they saw and heard concerning Jesus could remind each other in cases of dispute. In any case, Biblical sources (Acts 2, verses 5-11; 11, verses 19-20; 18 verses 1-2) and secular history make it clear that about 25 years after Jesus started his public ministry, many Christians were found all over the Eastern Mediterranean. They also spread to the West as far as Rome. Any changes to the Gospel would have been met with very fierce opposition from all these different parts of the world.