Internal consistency as proof

أَفَلَا يَتَدَبَّرُونَ ٱلْقُرْءَانَ ۚ وَلَوْ كَانَ مِنْ عِندِ غَيْرِ ٱللَّهِ لَوَجَدُوا۟ فِيهِ ٱخْتِلَـٰفًا كَثِيرًا

Then do they not reflect upon the Qur’ān? If it had been from [any] other than Allāh, they would have found within it much contradiction.