Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
muslim:811b – [Chain 1] Isḥāq b. Ibrāhīm > Muḥammad b. Bakr > Saʿīd b. Abū ʿArūbah [Chain 2] Abū Bakr b. Abū Shaybah > ʿAffān > Abān al-ʿAṭṭār Jamīʿ

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.  

مسلم:٨١١b – وَحَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ أَخْبَرَنَا مُحَمَّدُ بْنُ بَكْرٍ حَدَّثَنَا سَعِيدُ بْنُ أَبِي عَرُوبَةَ ح وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ حَدَّثَنَا عَفَّانُ حَدَّثَنَا أَبَانٌ الْعَطَّارُ جَمِيعًا

عَنْ قَتَادَةَ بِهَذَا الإِسْنَادِ وَفِي حَدِيثِهِمَا مِنْ قَوْلِ النَّبِيِّ ﷺ قَالَ إِنَّ اللَّهَ جَزَّأَ الْقُرْآنَ ثَلاَثَةَ أَجْزَاءٍ فَجَعَلَ قُلْ هُوَ اللَّهُ أَحَدٌ جُزْءًا مِنْ أَجْزَاءِ الْقُرْآنِ  

See similar narrations below:

Collected by Dārimī
darimi:3471 – Abū al-Mughīrah > Ṣafwān > Iyās al-Bikālī > Nawf al-Bikālī

[Machine] "Indeed, Allah has divided the Quran into three parts, and He made 'Say, He is Allah, the One' as one-third of the Quran."  

الدارمي:٣٤٧١ – حَدَّثَنَا أَبُو الْمُغِيرَةِ حَدَّثَنَا صَفْوَانُ حَدَّثَنَا إِيَاسٌ الْبِكَالِيُّ عَنْ نَوْفٍ الْبِكَالِيِّ قَالَ

«إِنَّ اللَّهَ جَزَّأَ الْقُرْآنَ عَلَى ثَلَاثَةِ أَجْزَاءٍ فَجَعَلَ قُلْ هُوَ اللَّهُ أَحَدٌ ثُلُثَ الْقُرْآنِ»