(69) باب صِيَامِ يَوْمِ عَاشُورَاءَ
Narrated Salama bin Al-Akwa`:
The Prophet (ﷺ) ordered a man from the tribe of Bani Aslam to announce amongst the people that whoever had eaten should fast the rest of the day, and whoever had not eaten should continue his fast, as that day was the day of 'Ashura' .
Reference: Sahih al-Bukhari 2007
In-book reference: Book 30, Hadith 112
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 31, Hadith 225