Sunan Abi Dawud 1461
سنن أبي داود#1461Sahihحَدَّثَنَا الْقَعْنَبِيُّ، عَنْ مَالِكٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ عَبْدِ اللَّهِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِيهِ، 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 وَكَانَ الرَّجُلُ يَتَقَالُّهَا فَقَالَ النَّبِيُّ صلى الله عليه وسلم " وَالَّذِي نَفْسِي بِيَدِهِ إِنَّهَا لَتَعْدِلُ ثُلُثَ الْقُرْآنِ " .
Abu Sa'id al-Khudri said:A man heard another man reciting "Say, He is Allah, One" He was repeating it. When the next morning came, he went to the Messenger of Allah (ﷺ) and mentioned to him. The man tool it (this surah) as a small one. The Prophet (ﷺ) said: By Him in Whose Hand is my life, it is equivalent to a third of the Qur'an
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: 8:46