Quran 16:103 — The Bee (Al-Nahl)

وَلَقَد نَعلَمُ أَنَّهُم يَقولونَ إِنَّما يُعَلِّمُهُ بَشَرٌ ۗ لِسانُ الَّذى يُلحِدونَ إِلَيهِ أَعجَمِىٌّ وَهٰذا لِسانٌ عَرَبِىٌّ مُبينٌ

We are fully aware that they say, "A human being is teaching him!" The tongue of the source they hint at is non-Arabic, and this is a perfect Arabic tongue.

[16:102] Say, "The Holy Spirit has brought it down from your Lord, truthfully, to assure those who believe, and to provide a beacon and good news for the submitters."

[16:104] Surely, those who do not believe in GOD's revelations, GOD does not guide them. They have incurred a painful retribution.