Quran’s message has no crookedness or contradictions
Allah ﷻ says in the Quran:
Do they not then consider the Quran carefully? Had it been from other than Allah, they would surely have found therein many a contradiction.
Quran (Surah An-Nisa, Verse 82)
He ﷻ also says:
“All the praises and thanks be to Allah, Who has sent down to His slave (Muhammad ﷺ ) the Book (the Quran), and has not placed therein any crookedness.”
Quran (Surah Al-Kahf, Verse 1)
Allah ﷻ makes it clear in the Quran that it could not have been revealed by anyone other than Him. He ﷻ says:
And this Qur’an is not such as could ever be produced by other than Allah (Lord of the heavens and the earth), but it is a confirmation of (the revelation) which was before it [i.e. the Taurat (Torah), and the Injeel (Gospel)], and a full explanation of the book (i.e. laws, decreed for mankind) – wherein there is no doubt – from the Lord of the ‘Alamin (mankind, jinn, and all that exists).