وَقالَ الَّذينَ كَفَروا لَولا نُزِّلَ عَلَيهِ القُرآنُ جُملَةً واحِدَةً ۚ كَذٰلِكَ لِنُثَبِّتَ بِهِ فُؤادَكَ ۖ وَرَتَّلناهُ تَرتيلًا

And those who disbelieve say, "Why was the Qur'an not revealed to him all at once?" Thus [it is] that We may strengthen thereby your heart. And We have spaced it distinctly.