SCHOLARS WHO SAY THAT THE VARIANT READINGS ARE ALL PART OF THE QUR'AN
This oral tradition (of the Qur'an) embraces ten distinct systems of recitation, or, as they are generally called among scholars, "Readings" (qiraa'aat), each tranmitted by a "school" of Koran-readers deriving its authority from a prominent reader of the second or early third century of the Islamic era. The slight variation among the Ten Readings is attributable to the dialectal variation in the original Revelation. ... It should be emphasized that all of the Readings were transmitted orally from the Prophet (Labib as-Said, The Recited Koran: A History of the First Recorded Version, translated by B. Weis, M. Rauf and M. Berger, Princeton, New Jersey: The Darwin Press, 1975, p. 53)
Every reading in accordance with Arabic (grammar) even if (only) in some way, and in accordance with one of the masaahif of Uthmaan, even if (only) probable, and with sound chain of transmission, is a correct (Sahiih) reading, which must not be rejected, and may not be denied, but it belongs to the seven modes (ahruf) according to which the Qur'aan was revealed, and the people are obliged to accept it, no matter whether it is from the seven Imaans, or the ten or from other accepted Imaans (Abu-l-Khair bin al-Jazari, cited from Ahmad von Denffer, Ulum Al-Qur'an, UK: The Islamic Foundation, 1994. p. 119)
SCHOLARS WHO SAY THAT THE VARIANT READINGS ARE FROM HUMAN ERROR
The Koran was originally recited in one language and one dialect, namely that of the Quraysh. However, as soon as readers from the different tribes began to recite it, a variety of readings emerged, reflecting dialectal differences among the readers. The diversity was so great that later generations of readers and scholars had to labor intensely over the recording and careful analysis of these readings. In so doing they give rise to a special science, or rather special sciences, devoted exclusively to this enterprise. ...
... I should pause here to note that certain religious authorities have supposed that the Seven Readings were transmitted by a process of continuous transmission (tawaatur) on a wide scale from the Prophet himself, unto whom, so they allege, they were revealed by Gabriel. These authorities therefore consider that whoever rejects any of the established readings is an unbeliever. They have not, however, been able to produce any evidence for what they claim except that the tradition which reads, "The Koran was revealed in seven dialects (ahruf)".
The truth of the matter is that the seven Readings had nothing to do with the Revelation, nothing in the least; and whoever rejects any of them is not for having done so an unbeliever; nor has he sinned or gone astray in his religion. The origin of these Readings is to be found in the diversity of tribal dialects among the early Muslim Arabs, and everyone has the right to dispute them, and to accept and reject them, or parts of them, as seems proper.
In point of fact, people have disputed the Readings and argued over them, and have even accused each other of error with respect to them; yet we know of no Muslim who ever charged another with unbelief over this matter (Taahaa Husayn, Fi'l-Adab al-jaahilii, pp. 98-99. Cited from Labib as-Said, The Recited Koran: A History of the First Recorded Version, translated by B. Weis, M. Rauf and M. Berger, Princeton, New Jersey: The Darwin Press, 1975, pp. 97-99) Before closing this note a few words about the recitations Qir'aat - It is generally known that there are seven or ten different recitations of the Qur'an - By recitation is meant the different wordings which convey the same or allied meanings Maalik and Malik - Such as Yatta'harna and Yat'harna. It is generally believed the recitation of the seven or the ten reciters of the first, second and third century of Islam are valid and the Muslims are allowed to adopt either of these in their reciting Qur'an and it is generally held that the origin of these various recitations go back to the time of the Holy Prophet who approved these varieties but according to the Shia Ithna-Ashari School whose views are based on the teachings of the Holy Imams, the revealed recitation of the Qur'an cannot be but one and as the Imam puts it, "Qur'an is One, came down from the One, the variation in recitation comes from the reciters not from God." (S. V. Mir Ahmed Ali, The Holy Qur'an: Text, Translation and Commentary, New York: Tahrike Tarsile Qur'an, 1988, p. 58a)