Unmistakably from Allah

69:38-47 (Pickthall tr.)

But nay! I swear by all that ye see
And all that ye see not
That it is indeed the speech of an illustrious messenger.
It is not poet's speech - little is it that ye believe!
Nor diviner's speech - little is it that ye remember!
It is a revelation from the Lord of the Worlds.
And if he had invented false sayings concerning Us,
We assuredly had taken him by the right hand
And then severed his life-artery,
And not one of you could have held Us off from him.

‏فَلَآ أُقْسِمُ بِمَا تُبْصِرُونَ
‏وَمَا لَا تُبْصِرُونَ
إِنَّهُۥ لَقَوْلُ رَسُولٍۢ كَرِيمٍۢ
وَمَا هُوَ بِقَوْلِ شَاعِرٍۢ ۚ قَلِيلًۭا مَّا تُؤْمِنُونَ
‏وَلَا بِقَوْلِ كَاهِنٍۢ ۚ قَلِيلًۭا مَّا تَذَكَّرُونَ
تَنزِيلٌۭ مِّن رَّبِّ ٱلْعَلَمِينَ
وَلَوْ تَقَوَّلَ عَلَيْنَا بَعْضَ ٱلْأَقَاوِيلِ
‏لَأَخَذْنَا مِنْهُ بِٱلْيَمِينِ
‏ثُمَّ لَقَطَعْنَا مِنْهُ ٱلْوَتِينَ
‏فَمَا مِنكُم مِّنْ أَحَدٍ عَنْهُ حَجِزِينَ
‏