(69) باب صِيَامِ يَوْمِ عَاشُورَاءَ
Narrated Salim's father:
The Prophet (ﷺ) said, "Whoever wishes may fast on the day of 'Ashura'."
Reference: Sahih al-Bukhari 2000
In-book reference: Book 30, Hadith 105
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 31, Hadith 218