Muwatta Malik 488
موطأ مالك#488SahihThese are the words of a Successor — the generation after the Companions — not of the Prophet ﷺ.
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ، أَنَّهُ أَخْبَرَهُ أَنَّ {قُلْ هُوَ اللَّهُ أَحَدٌ} تَعْدِلُ ثُلُثَ الْقُرْآنِ وَأَنَّ {تَبَارَكَ الَّذِي بِيَدِهِ الْمُلْكُ} تُجَادِلُ عَنْ صَاحِبِهَا .
Yahya related to me from Malik from Ibn Shihab that Humayd ibn Abd ar-Rahman ibn Awf had told him that Surat al-Ikhlas (Sura 112) was equal to a third of the Qur'an, and that Surat al-Mulk (Sura 67) pleaded for its owner
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 15:19