أَمْ يَقُولُونَ افْتَرَاهُ ۖ قُلْ فَأْتُوا بِعَشْرِ سُوَرٍ مِثْلِهِ مُفْتَرَيَاتٍ وَادْعُوا مَنِ اسْتَطَعْتُمْ مِنْ دُونِ اللَّهِ إِنْ كُنْتُمْ صَادِقِينَ
Or they may say, "He forged it," Say, "Bring ye then ten suras forged, like unto it, and call (to your aid) whomsoever ye can, other than Allah!- If ye speak the truth! 
فَإِلَّمْ يَسْتَجِيبُوا لَكُمْ فَاعْلَمُوا أَنَّمَا أُنْزِلَ بِعِلْمِ اللَّهِ وَأَنْ لَا إِلَٰهَ إِلَّا هُوَ ۖ فَهَلْ أَنْتُمْ مُسْلِمُونَ
"If then they (your false gods) answer not your (call), know ye that this revelation is sent down (replete) with the knowledge of Allah, and that there is no god but He! will ye even then submit (to Islam)?"