16:103 wa laqad na'Ålamu an-nahum yaquuluuna in-namaa yu'Al-limuhuu bashar* lisaanul-ladhiy yulHiduuna ilayhi a'Åjamiy-yuw wa haadhaa lisaanun 'Arabiy-yum mubiyn

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Ahmed Raza Khan: Mohammed Aqib Qadri:
And indeed We know that they say, "This Qur’an is being taught by some other man"; the one they refer to speaks a foreign language, whereas this is clear Arabic!

Yusuf Ali:
We know indeed that they say, "It is a man that teaches him." The tongue of him they wickedly point to is notably foreign, while this is Arabic, pure and clear.

Pickthal:
And We know well that they say: Only a man teacheth him. The speech of him at whom they falsely hint is outlandish, and this is clear Arabic speech.