Sahih Muslim 1843
صحيح مسلم#1843Sahihوَحَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمٍ، حَدَّثَنَا مُحَمَّدُ بْنُ بَكْرٍ، أَخْبَرَنَا ابْنُ جُرَيْجٍ، حَدَّثَنِي عَبْدَةُ، بْنُ أَبِي لُبَابَةَ عَنْ شَقِيقِ بْنِ سَلَمَةَ، قَالَ سَمِعْتُ ابْنَ مَسْعُودٍ، يَقُولُ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " بِئْسَمَا لِلرَّجُلِ أَنْ يَقُولَ نَسِيتُ سُورَةَ كَيْتَ وَكَيْتَ أَوْ نَسِيتُ آيَةَ كَيْتَ وَكَيْتَ بَلْ هُوَ نُسِّيَ " .
Ibn Mas'ud reported Allah's Messenger (ﷺ) as saying:Wretched is the man who says: I forgot such and such a sura, or I forget such and such a verse, but he has been made to forget
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:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 6:271