وَإِن كُنتُم في رَيبٍ مِمّا نَزَّلنا عَلىٰ عَبدِنا فَأتوا بِسورَةٍ مِن مِثلِهِ وَادعوا شُهَداءَكُم مِن دونِ اللَّهِ إِن كُنتُم صادِقينَ

And if you are in doubt about what We have sent down upon Our Servant [Muhammad], then produce a surah the like thereof and call upon your witnesses other than Allah, if you should be truthful.