Al-Furqan 25:32

وَقَالَ ٱلَّذِينَ كَفَرُوا۟ لَوْلَا نُزِّلَ عَلَيْهِ ٱلْقُرْءَانُ جُمْلَةً وَٰحِدَةً ۚ كَذَٰلِكَ لِنُثَبِّتَ بِهِۦ فُؤَادَكَ ۖ وَرَتَّلْنَـٰهُ تَرْتِيلًا

Waqāla alladhīna kafarū lawlā nuzzila ʿalayhi l-qur'ānu jum'latan wāḥidatan kadhālika linuthabbita bihi fuādaka warattalnāhu tartīlan

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