(20) باب أَىُّ يَوْمٍ يُصَامُ فِي عَاشُورَاءَ
Abdullah b 'Abbas reported that the Messenger of Allah (ﷺ) had said:
If I live till the next (year), I would definitely observe fast on the 9th, and the narration transmitted by Abu Bakr is:" He meant the day of Ashura." (ES)
Reference (ES): Sahih Muslim 1134 b (ES)
In-book reference (ES): Book 13, Hadith 173 (ES)
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2529 (ES)