The Qur’an has reached us through tawatur (Arabic for: transmission by successive generations); that is a large number of those who received it directly from Prophet Muhammad (peace and blessings be upon him) had learned it by heart and recorded it in writing. Thus, the possibility of them agreeing on falsification did not exist. So, the Qur’an that we have today is letter by letter the original, divine revelation sent to the Prophet (peace and blessings be upon him).
Consensus of the Muslim Ummah has always existed regarding this for over 14 centuries. Consequently, anyone who rejects even a single Qur’anic verse is in fact rejecting a firmly established matter in religion that is unanimously agreed upon among all the Muslim Ummah.
The eminent Muslim scholar and renowned da`iyah`Abdel Khaliq Hasan Ash-Shareef states: It should be clear that there were hundreds of the Companions of the Prophet (peace and blessings be upon him) who were learning the whole Qur’an by heart. When it was decided to compile the Qur’an by the help of those who had been writing down the Qur’an under direct supervision from the Prophet, each scribe who wrote down any verse of the Qur’an was asked to provide a witness to give testimony that he saw him writing down the verse in front of the Prophet (peace and blessings be upon him).

As for the two verses mentioned, it was Khuzaymah who wrote down these verses and he failed to come with a witness to support him. However, they were accepted from Khuzaymah because the Prophet (peace and blessings be upon him) is reported to have said that Khuzayma’s testimony equals the testimony of two witnesses. So, the debate was not on whether they belong to the Qur’an or not as they were known and well memorized by memorizers of the Qur’an from among the Companions. But the debate was on providing a witness that he wrote them down between the hands of the Prophet (peace and blessings be upon him).