As mentioned above, the Shi‘a deny any alteration in the Qur’an and believe that the Qur’an available today is the same that was revealed to the Prophet Muhammad. The Qur’an is complete. No one has ever seen a copy of the Qur’an different from the standard one in any part of the Islamic world. There are manuscripts of the Qur’an available today that go back to the time of Shi‘a Imams and they are exactly the same as the current ones.
The Glorious Qur’an itself explicitly says that God Himself preserves the Qur’an from any alteration and distortion:
Surely We have revealed the Reminder and We will most surely be its preserver. (15:9)1
Regarding this verse, ‘Allamah Tabataba’i in his renowned Al-Mizan fi Tafsir al-Qur’an, one of the greatest commentaries of the Qur’an, states:
…the Qur’an is a living and eternal Reminder which will never die and fall into oblivion. It is immune from any addition and loss. It is immune from and secure against any alterations in form and style which could affect its character and role, that is, as, “the Reminder of Allah which expresses divine truth and knowledge”. For this reason, the aforesaid verse indicates that the divine Book has always been and will continue to be guarded against any distortion and alteration.2
1 It should be noted that the charge with belief in alteration is limited to deletion of some alleged verses; otherwise neither the Shi‘a nor the Sunni Muslims have ever been charged with belief in addition to the Qur’an. Therefore, one can argue from the Qur’anic verses for refutation of the idea of alteration.
2 Al-Mizan fi Tafsir al-Qur’an, vol. 12, p. 99.
Discovering Shi’i Islam Mohammad Ali Shomali 9th edition