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 77
Narrated Abu Sa’id Al-Khudrī, “A man heard another man reciting (Sūrah Al-Ikhlāṣ) ‘Say He is Allah, (the) One.’ repeatedly. The next morning, he came to Allah’s Messenger ﷺ and informed him about it as if he thought that it was not enough to recite. On that Allah’s Messenger ﷺ said, “By Him in Whose Hand my life is, this Sūrah is equal to one-third of the Qur’an!” Reference: Sahih al-Bukhari 5013.
عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، أَنَّ رَجُلاً، سَمِعَ رَجُلاً، يَقْرَأُ (‏قُلْ هُوَ اللَّهُ أَحَدٌ‏)‏ يُرَدِّدُهَا فَلَمَّا أَصْبَحَ جَاءَ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَذَكَرَ ذَلِكَ لَهُ وَكَأَنَّ الرَّجُلَ يَتَقَالُّهَا فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ وَالَّذِي نَفْسِي بِيَدِهِ إِنَّهَا لَتَعْدِلُ ثُلُثَ الْقُرْآنِ ‏".‏‏.
Reference : Virtues of the Qur'an's Chapters and Verses 77