The Quran serves as a quality control agent, determining which parts of the Bible are true and which have been corrupted.

The Quran explicitly states that it confirms and bears witness to the authority of the Holy Bible, as seen in Surah 5:48. This verse indicates that the Scriptures in use at the time of Muhammad were authentic and genuine, given by God himself. If the Quran is indeed a custodian of the previous Scriptures, it must affirm their integrity and reliability. Furthermore, the same expressions used in the Quran to describe the Old and New Testaments suggest that they were to be regarded as the absolute test of right and wrong. Thus, the assertion that the Quran only validates the Bible when it agrees with its teachings contradicts its own claim to be a witness to the truth of the Scriptures. The historical continuity of the Bible, supported by manuscripts and translations, further reinforces the argument that the Scriptures have remained unchanged since the seventh century, as indicated by the Quran's own testimony.