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 78
This hadith has been narrated by Qatada with the same chain of transmitters in these words:
He (the Messenger of Allah) said: Allah divided the Qur'an into three parts, and he made:" Say: He, Allah is One." one part out of the (three) parts of the Qur'an.” Reference: Sahih Muslim 811b.
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَفَّانُ، حَدَّثَنَا أَبَانٌ الْعَطَّارُ، جَمِيعًا عَنْ قَتَادَةَ، بِهَذَا الإِسْنَادِ ‏.‏ وَفِي حَدِيثِهِمَا مِنْ قَوْلِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ إِنَّ اللَّهَ جَزَّأَ الْقُرْآنَ ثَلاَثَةَ أَجْزَاءٍ فَجَعَلَ قُلْ هُوَ اللَّهُ أَحَدٌ جُزْءًا مِنْ أَجْزَاءِ الْقُرْآنِ ‏"‏.‏
Reference : Virtues of the Qur'an's Chapters and Verses 78