Sura al-Naḥl 16:103

وَلَقَدْ نَعْلَمُ أَنَّهُمْ يَقُولُونَ إِنَّمَا يُعَلِّمُهُۥ بَشَرٌ لِّسَانُ ٱلَّذِى يُلْحِدُونَ إِلَيْهِ أَعْجَمِىٌّ وَهَٰذَا لِسَانٌ عَرَبِىٌّ مُّبِينٌ

wa-la-qad naʿlamu annahum yaqūlūna innamā yuʿallimuhu basharun llisānu alladhī yulḥidūna ilayhi aʿjamiyyun wa-hādhā lisānun ʿarabiyyun mubīnun

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.

Sura al-Shuʿarā 26:198

وَلَوْ نَزَّلْنَٰهُ عَلَىٰ بَعْضِ ٱلْأَعْجَمِينَ

wa-law nazzalnāhu ʿalā baʿḍi l-aʿjamīna

Had We revealed it to any of the non-Arabs,

Sura Fuṣṣilat 41:44

وَلَوْ جَعَلْنَٰهُ قُرْءَانًا أَعْجَمِيًّا لَّقَالُوا۟ لَوْلَا فُصِّلَتْ ءَايَٰتُهُۥٓ ءَا۬عْجَمِىٌّ وَعَرَبِىٌّ قُلْ هُوَ لِلَّذِينَ ءَامَنُوا۟ هُدًى وَشِفَآءٌ وَٱلَّذِينَ لَا يُؤْمِنُونَ فِىٓ ءَاذَانِهِمْ وَقْرٌ وَهُوَ عَلَيْهِمْ عَمًى أُو۟لَٰٓئِكَ يُنَادَوْنَ مِن مَّكَانٍۭ بَعِيدٍ

wa-law jaʿalnāhu qurʾānan aʿjamiyyan llaqālū lawlā fuṣṣilat āyātuhu aʿjamiyyun wa-ʿarabiyyun qul huwa li-lladhīna āmanū hudan wa-shifāʾun wa-lladhīna lā yuʾminūna fī ādhānihim waqrun wa-huwa ʿalayhim ʿaman ulāʾika yunādawna min makānin baʿīdin

Had We sent this as a Qur'an (in the language) other than Arabic, they would have said: "Why are not its verses explained in detail? What! (a Book) not in Arabic and (a Messenger an Arab?" Say: "It is a Guide and a Healing to those who believe; and for those who believe not, there is a deafness in their ears, and it is blindness in their (eyes): They are (as it were) being called from a place far distant!"