الجامع المختصر لفضائل الآيات والسور
Virtues of the Qur'an's Chapters and Verses
This sūrah is equivalent to one-third of the Qur'ān
تَعْدِلُ هَذِهِ السُّورَةُ ثُلُثَ الْقُرْآنِ
Virtues of the Qur'an's Chapters and Verses 76
The Prophet ﷺ asked:
“Is any one of you unable to recite one-third of the Qur'ān in one night? They said: How could anyone read one-third of the Qur'ān (in one night)? He said: Qul huwa Allāhu aḥad (Sūrat al-Ikhlāṣ) is equivalent to one-third of the Qur'ān.” Reference: Sahih Muslim 811a.
عَنْ أَبِي الدَّرْدَاءِ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ أَيَعْجِزُ أَحَدُكُمْ أَنْ يَقْرَأَ فِي لَيْلَةٍ ثُلُثَ الْقُرْآنِ ‏" قَالُوا : وَكَيْفَ يَقْرَأْ ثُلُثَ الْقُرْآنِ؟ قَالَ : " قُلْ هُوَ اللَّهُ أَحَدٌ تَعْدِلُ ثُلُثَ الْقُرْآنِ " ‏.‏
Reference : Virtues of the Qur'an's Chapters and Verses 76