Hadith 2370
Chapter 70: The fast of the Prophet - كتاب الصيام
أَخْبَرَنَا 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.'
Reference : Sunan an-Nasa'i 2370
In-book reference : Book 22, Hadith 281