We know that they say a mere mortal has taught it (the Quran) to him (Muhammad). The language of the person whom they think has taught it to him is not Arabic. This (the Quran) is in illustrious Arabic.
و هر آينه مى‌دانيم كه آنان مى‌گويند: آدميى به او مى‌آموزد زبان آن كس كه [اين قرآن را] به او نسبت مى‌دهند گنگ و نارساست و اين [قرآن‌] به زبان تازى روشن است.