The Prophet ﷺ said to his companions, "Is any of you unable to recite a third of the Quran in a single night?"This was difficult for them, and they said, "Which of us could manage that, Messenger of Allah?"He replied, "Allah, the One, the Eternal Refuge is a third of the Quran."
قال النبي ﷺ لأصحابه: أيعجز أحدكم أن يقرأ ثلث القرآن في ليلة؟ فشق ذلك عليهم، وقالوا: أينا يطيق ذلك يا رسول الله؟ فقال: الله الواحد الصمد ثلث القرآن.
Bukhari narrated it in the Virtues of the Quran (5015) from Umar bin Hafs, who said, my father narrated to us, Amash narrated to us, Dahhak Mashriqi narrated to us, from Abu Saeed Khudri, and he related it.