Surah Al-Baqarah, Verse 23

وَإِن كُنتُمۡ فِي رَيۡبٖ مِّمَّا نَزَّلۡنَا عَلَىٰ عَبۡدِنَا فَأۡتُواْ بِسُورَةٖ مِّن مِّثۡلِهِۦ وَٱدۡعُواْ شُهَدَآءَكُم مِّن دُونِ ٱللَّهِ إِن كُنتُمۡ صَٰدِقِينَ٢٣

wa-in kuntum fī raybin mimmā nazzalnā ʿalā ʿabdinā fatū bisūratin min mith'lihi wa-id'ʿū shuhadāakum min dūni l-lahi in kuntum ṣādiqīna

And if you are in doubt about what We have sent down [i.e., the Qur’ān] upon Our Servant [i.e., Prophet Muḥammad (ﷺ)], then produce a sūrah the like thereof and call upon your witnesses [i.e., supporters] other than Allāh, if you should be truthful.