وَلَقَد نَعلَمُ أَنَّهُم يَقولونَ إِنَّما يُعَلِّمُهُ بَشَرٌ ۗ لِسانُ الَّذي يُلحِدونَ إِلَيهِ أَعجَمِيٌّ وَهـٰذا لِسانٌ عَرَبِيٌّ مُبينٌ

And We certainly know that they say, "It is only a human being who teaches the Prophet." The tongue of the one they refer to is foreign, and this Qur'an is [in] a clear Arabic language.