The Quran Verses:
Surah 6:34:
...And there is none who can alter the words of Allah...Surah 6:115:
And the word of your Lord has been fulfilled in truth and in justice. None can alter His words, and He is the Hearing, the Knowing.
The Relevant Source Text (Internal Quranic Contradiction):
Surah 2:106:
We do not abrogate a verse or cause it to be forgotten except that We bring forth better than it or similar to it. Do you not know that Allah is over all things competent?Surah 16:101:
And when We substitute a verse in place of a verse - and Allah is most knowing of what He sends down - they say, "You are but an inventor."
Surah 6 lays down a foundational theological rule: NO ONE can alter the words of Allah.
However, as Muhammad's political and military situation changed in Medina, the doctrine of "Naskh" (Abrogation) was introduced.
God supposedly began substituting, deleting, and replacing his own verses (such as changing the direction of prayer from Jerusalem to Mecca, or shifting from peaceful tolerance to military conquest).
To the critical scholar, Surah 6:115 represents the original claim of a fixed divine message, while Surah 2:106 is a later, pragmatic human invention designed to explain away the inconsistencies and changing rules within the expanding text.