we know that they say a mere mortal has taught it to him . the language of the person whom they think has taught it to him is not arabic. this is in illustrious arabic.
ولقد نعلم أنهم يقولون إنما يعلمه بشر لسان الذي يلحدون إليه أعجمي وهذا لسان عربي مبين