(Hood) 11 : 13
أَمْ يَقُولُونَ افْتَرَاهُ ۖ قُلْ فَأْتُوا بِعَشْرِ سُوَرٍ مِثْلِهِ مُفْتَرَيَاتٍ وَادْعُوا مَنِ اسْتَطَعْتُمْ مِنْ دُونِ اللَّهِ إِنْ كُنْتُمْ صَادِقِينَ
Or do they say: “He forged it”; You say: “Then you bring ten Sura like It that have been forged, and you call upon whomever you can besides Lord Allah if you are so truthful”.
It is told in verse 32:3: “Nay, It is the Truth from your Lord for you to warn a people to whom no warner has come before you so that they may be guided.” See explanation 2:23-24 and 10:37-38.