(19) باب صَوْمِ يَوْمِ عَاشُورَاءَ
Ibn Abbas was asked about observing of fast on the day of Ashura, whereupon he said:
I do not know Allah's Messenger (ﷺ) singling out any day's fast and considering it more excellent than another, except this day (the day of Ashura) and this month, meaning the month of Ramadan.
Reference: Sahih Muslim 1132 a
In-book reference: Book 13, Hadith 168
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2524