Verse 38

أَمْ يَقُولُونَ ٱفْتَرَىٰهُ قُلْ فَأْتُوا۟ بِسُورَةٍ مِّثْلِهِۦ وَٱدْعُوا۟ مَنِ ٱسْتَطَعْتُم مِّن دُونِ ٱللَّهِ إِن كُنتُمْ صَـٰدِقِينَ

Are they saying that he fabricated it? Say, then bring one chapter like this and call upon whomever you can find beside God, if you are truthful.