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

We know they say, “A human is teaching him.” The language of the one they maliciously allude to is foreign, yet this is in clear Arabic.