[Chapter 2: The Cow, Al-Baqara, الْبَقَرَة : Verse 23]
وَإِن كُنتُمْ فِي رَيْبٍ مِّمَّا نَزَّلْنَا عَلَىٰ عَبْدِنَا فَأْتُوا بِسُورَةٍ مِّن مِّثْلِهِ وَادْعُوا شُهَدَاءَكُم مِّن دُونِ اللَّهِ إِن كُنتُمْ صَادِقِينَ
[2:23] And if you are in doubt as to what We have sent down to Our servant, then bring a surah like this, and call upon your witnesses other than God if you are truthful.
[Chapter 11: Hud, Hud, هُوْد : Verse 13]
أَمْ يَقُولُونَ افْتَرَاهُ قُلْ فَأْتُوا بِعَشْرِ سُوَرٍ مِّثْلِهِ مُفْتَرَيَاتٍ وَادْعُوا مَنِ اسْتَطَعْتُم مِّن دُونِ اللَّهِ إِن كُنتُمْ صَادِقِينَ
[11:13] Or do they say: "He has invented it!" Say: "Then bring ten invented surahs like it, and call on whom you can besides God if you are truthful."