Those who disbelieved said, “Why did not the Quran come through him all at once?” We have released it to you gradually, in order to fix it in your memory. We have recited it in a specific sequence.
وَقالَ الَّذينَ كَفَروا لَولا نُزِّلَ عَلَيهِ القُرءانُ جُملَةً وٰحِدَةً كَذٰلِكَ لِنُثَبِّتَ بِهِ فُؤادَكَ وَرَتَّلنٰهُ تَرتيلًا
wa qaalal lazeena kafaroo law laa nuzzila ‘alaihil Qur’aanu jumlatanw waahidah; kazaalika linusabbita bihee fu’aadaka wa rattalnaahu tarteelaa