The Women - 4:82
Do they not examine the Qur´an? Had it belonged to anyone other than Allah, they would have found many contradictions in it.
Related:
The Cave/18:1
Praise be to Allah, Who has sent down the Book to His servant and has left no crookedness in it.
The Companies/39:23
Allah has sent down the best hadith in a coherent book in two parts. The skins of those who honor their Lord tremble because of it. Then their skins and hearts soften towards the message of Allah. This is Allah´s guidance; He guides whom He wills and/or guides whom He wills to it. There is no guidance for anyone whom Allah leads astray
The Women/4:82
Do they not examine the Qur´an? Had it belonged to anyone other than Allah, they would have found many contradictions in it.