It is true that Prophet Muhammad (peace and blessings be upon him) received his first revelation in his fortieth year. And it is true that both the books of the Bible and the Quran cover much common ground.

It is also true that in the course of 23 years, verses were revealed to Prophet Muhammad (peace and blessings be on him) on different occasions and that he asked his followers to put these verses in particular places in different chapters. All this is true.

But the conclusion of the Christian critics that the Prophet had been memorizing Biblical verses during the first 40 years of his life in order to fabricate the Quran is untenable for the following reasons:

There was no Arabic translation of the Bible available during the Prophet’s time. For a detailed account of this subject, read the article:

Ernst Würthwein informs us in his book, The Text Of The Old Testament:

“With the victory of Islam the use of Arabic spread widely and for Jews and Christians in the conquered lands it became the language of daily life. This gave rise to the need of Arabic versions of the Bible, which need was met by a number of versions mainly independent and concerned primarily for interpretation.” (Ernst Würthwein, The Text Of The Old Testament (Grand Rapids, Michigan: William B. Eerdmans Publishing Company, 1988, pp. 104.)

Thus, the first translations of the Hebrew Bible in Arabic appeared after the advent of Islam. In fact, the oldest dated manuscript of the Old Testament in Arabic dates from the first half of the ninth century.

What about the New Testament?

Sidney H Griffith, who has done extensive research on the appearance of Arabic and the New Testament says:
“The oldest dated manuscript containing the Gospels in Arabic is Sinai Arabic MS 72. Here the text of the four canonical Gospels is marked off according to the lessons of the temporal cycle of the Greek liturgical calendar of the Jerusalem Church.  

A colophon informs us that the MS was written by Stephen of Ramleh in the year 284 of the Arabs, i.e., 897 AD.” (Sidney H Griffith, The Gospel in Arabic: An Enquiry into Its Appearance in the First Abbasid Century, Oriens Christianus, Volume 69, p. 131-132.)

It is well-known that the Prophet did not know how to read or write: he was illiterate. So there was no question of his plagiarizing the Bible, even if an Arabic copy did in fact exist in his time. What then of the charge that he was taught by some Christians?

Allah the Almighty answered the criticism fourteen centuries ago in these verses, which say what means:

 To deny the divine origin of the Quran missionaries claim that Muhammad (peace and blessings be upon him) knew all the sources—Christian, Jewish, Zoroastrian, Hanif and ancient Arab beliefs—before he compiled the Quran. However, this ignores the simple fact of his illiteracy that was even acknowledged by the enemies of Islam 1400 years ago. Allah the Almighty also answered this in the Quran, when it says what means:

Despite all this, the missionaries have been repeating the same arguments, hoping to mislead the gullible. It was common knowledge in Makkah that the Prophet was illiterate, and there is no record of the pagan Arabs in Makkah accusing Muhammad (peace be upon him) of not being illiterate.

The reasons why the whole of the Quran was not revealed to the Prophet at one time are well known: (1) It was only reasonable and realistic to reveal the guidance of Allah governing the individual and social lives of the gradually evolving Muslim society at the same pace as its stage-by-stage emergence in space and time. So verses had to be revealed to the Prophet depending upon the contexts demanding divine guidance.

(2) It was easier for the Prophet and his Companions to learn and imbibe the Quranic message as it was being revealed in small portions.

You also ask, “If the Prophet was asked by Allah to seek forgiveness, as is mentioned in the Quran, how can the Muslims believe that he was sinless?”

Please understand that Muslims do not believe that Muhammad (peace be on him) or any prophet for that matter was anything more than human. In this way we need not have any problem in recognizing any weakness in them that is characteristic of humans.

But it is part of our belief that all prophets were protected by Allah from the usual failings of ordinary humans. Bear in mind that this is true not only of Muhammad, but also of all prophets including Abraham, Moses, and Jesus (peace and blessings be on them all).

Muhammad (peace and blessings be on him), as well as all other prophets, was a model for all humans in all walks of life. Only a human who is like all other humans can serve as a model for other humans. That is why most Christians who imagine Jesus to be God cannot emulate his life as perceived by the Christians.

For instance, Jesus is reported to have fasted forty days and forty nights continuously. Can this form of fasting be an example for others to follow? It is important to note that the fasting of Muhammad is being followed by millions of his followers until today.

Allah says in the Quran that if He wanted to give humankind what they actually deserved, nobody would remain on the face of the earth. But Allah is All-Merciful. Islam is meant for humans, and it is clearly stated in the Quran that Allah created humans as weak creatures. The Quran says what means:

So it is only natural that humans need divine guidance to keep themselves free from sins. And Allah in His infinite mercy allows us to continue to live here even after we disobey Him again and again. Now the life of a prophet is a practical demonstration of how to live according to divine guidance.

Allah taught the prophet not only to do good things, but to avoid all bad things and to seek His forgiveness for any mistakes or lapses on his part as a human being. So no one, not even the Prophet, is exempt from seeking Allah’s forgiveness. And that is the reason why Muhammad (peace be upon him) was asked to seek Allah’s forgiveness. May Allah forgive us all and show us the right way!