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
nasai-kubra:10466 – Asmaʿ > Ibn al-Qāsim > Mālik > Ibn Shihāb > Ḥumayd b. ʿAbd al-Raḥman

[Machine] He informed him that "Say, 'He is Allah, the One'" [Surah Al-Ikhlas: 1] is one-third of the Quran.  

الكبرى للنسائي:١٠٤٦٦ – الْحَارِثُ بْنُ مِسْكِينٍ قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ عَنِ ابْنِ الْقَاسِمِ قَالَ حَدَّثَنِي مَالِكٌ عَنِ ابْنِ شِهَابٍ عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ

أَنَّهُ أَخْبَرَهُ أَنَّ {قُلْ هُوَ اللهُ أَحَدٌ} [الإخلاص 1] ثُلُثُ الْقُرْآنِ  

See similar narrations below:

Collected by Nasāʾī's Kubrá, Suyūṭī
nasai-kubra:10448 – Muḥammad b. al-Muthanná > Muḥammad > Shuʿbah > Manṣūr > Hilāl > Rabīʿ b. Khuthaym > ʿAmr b. Maymūn > Āmraʾah > Abū Ayyūb

[Machine] On the authority of the Prophet ﷺ , he said, "Say, 'He is Allah, [who is] One.'" (Surah Al-Ikhlas, verse 1) This verse constitutes one-third of the Quran.  

الكبرى للنسائي:١٠٤٤٨ – أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى قَالَ حَدَّثَنَا مُحَمَّدٌ قَالَ حَدَّثَنَا شُعْبَةُ عَنْ مَنْصُورٍ عَنْ هِلَالٍ عَنْ رَبِيعِ بْنِ خُثَيْمٍ عَنْ عَمْرِو بْنِ مَيْمُونٍ عَنِ امْرَأَةٍ عَنْ أَبِي أَيُّوبَ

عَنِ النَّبِيِّ ﷺ قَالَ {قُلْ هُوَ اللهُ أَحَدٌ} [الإخلاص 1] ثُلُثُ الْقُرْآنِ  

nasai-kubra:10457 – ʿAlī b. Saʿīd b. Masrūq al-Kūfī > ʿAbd al-Raḥīm > Zakariyyā > Abū Isḥāq > ʿAmr b. Maymūn > Baʿḍ Aṣḥāb Muḥammad ﷺ

[Machine] "The Prophet ﷺ said: 'Say, He is Allah, [who is] One.' (Surah Al-Ikhlas, verse 1) It is one-third of the Quran."  

الكبرى للنسائي:١٠٤٥٧ – أَخْبَرَنَا عَلِيُّ بْنُ سَعِيدِ بْنِ مَسْرُوقٍ الْكُوفِيُّ قَالَ حَدَّثَنَا عَبْدُ الرَّحِيمِ عَنْ زَكَرِيَّا عَنْ أَبِي إِسْحَاقَ عَنْ عَمْرِو بْنِ مَيْمُونٍ قَالَ حَدَّثَنِي بَعْضُ أَصْحَابِ مُحَمَّدٍ ﷺ

أَنَّ النَّبِيَّ ﷺ قَالَ {قُلْ هُوَ اللهُ أَحَدٌ} [الإخلاص 1] ثُلُثُ الْقُرْآنِ