ولقد نعلم أنهم يقولون إنما يعلمه بشر لسان الذي يلحدون إليه أعجمي (16:103) بالانجليزي

(16:103) We know very well what they say about you: "Surely a certain person teaches him. " *107 But the person to whom they allude speaks a foreign tongue, and this (Qur'an) is in plain Arabic.

Tafseer Abu-al-A'la Maududi

Page 279 English Traditional

*107) In this connection, traditions mention the names of several persons, one of whom (Jabar), according to the disbelievers of Makkah taught the Holy Prophet; however, one thing particularly noteworthy about all these persons is that they were non-Arab slaves. Whosoever he might be, the fact that he used to recite the Torah and the Gospel and had an acquaintance with the Holy Prophet, gave an opportunity to the disbelievers for spreading this false report that it was the particular slave who was the real author of the Holy Qur'an, but Muhammad (Allah's peace be upon him) presented it as the Word of God. This not only shows that his opponents were very impudent in spreading false accusations against the Holy Prophet but also that, in general, people are not just in judging the worth of their contemporaries. They were ill-treating like this that great personality who has had no parallel in history. Nevertheless, these people who had become blind in their opposition, preferred to attribute the authorship of the matchless Arabic Qur'an to a non-Arab slave who had a smattering of the Torah and the Gospel. Instead of accepting the claim of the Holy Prophet, who was an embodiment of truth, they attributed its authorship to an insignificant foreign slave.