﴿ أَمْ يَقُولُونَ ٱفْتَرَىٰهُ ۖ قُلْ فَأْتُوا۟ بِعَشْرِ سُوَرٍۢ مِّثْلِهِۦ مُفْتَرَيَٰتٍۢ وَٱدْعُوا۟ مَنِ ٱسْتَطَعْتُم مِّن دُونِ ٱللَّهِ إِن كُنتُمْ صَٰدِقِينَ ﴾

“and so they assert, "[Muhammad himself] has invented this [Qur'an)!" Say [unto them]: "Produce, then, ten surahs of similar merit, invented [by yourselves], and [to this end] call to your aid whomever you can, other than, God, if what you say is true!”

Please check ayah 11:14 for complete tafsir.