Sunan an-Nasa'i 2370
سنن النسائي#2370Sahihأَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ عُبَيْدِ اللَّهِ، أَنَّهُ سَمِعَ ابْنَ عَبَّاسٍ، وَسُئِلَ، عَنْ صِيَامِ، عَاشُورَاءَ قَالَ مَا عَلِمْتُ النَّبِيَّ صلى الله عليه وسلم صَامَ يَوْمًا يَتَحَرَّى فَضْلَهُ عَلَى الأَيَّامِ إِلاَّ هَذَا الْيَوْمَ يَعْنِي شَهْرَ رَمَضَانَ وَيَوْمَ عَاشُورَاءَ .
It was narrated from 'Ubaidullah that:he heard Ibn 'Abbas, when he was asked about the fast of 'Ashura' say: "I do not know that the Prophet fasted any day because of its virtue, except this day" meaning the month of Ramadan and the day of Ashura
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: 22:281