Al-Mukhtasar
وَقَالَ ٱلَّذِينَ كَفَرُوا۟ لَوْلَا نُزِّلَ عَلَيْهِ ٱلْقُرْءَانُ جُمْلَةً وَٰحِدَةً ۚ كَذَٰلِكَ لِنُثَبِّتَ بِهِۦ فُؤَادَكَ ۖ وَرَتَّلْنَـٰهُ تَرْتِيلًا ﴿٣٢﴾
Those who disbelieved in Allah said, ‘Why was the Qur’ān not sent down to him all at once instead of in bits and pieces?’ I sent the Qur’ān bit by bit to strengthen your heart - O Messenger - by its revelation time after time. I revealed it bit by bit to you to make it easy for you to understand and memorise it.