Answered by our Shaykh, the ‘Allaamah, the Sincere Adviser, Abu ‘Abdirrahman Yahya bin ‘Ali Al-Hajoori – may Allaah preserve him –
Has there come mention of any virtue in regards to the fasting the 9th & 10th of Muharram?
Yes, the statement of the Prophet ﷺ:
(لئن بقيت إلى قابل لأصمومن التاسع)
“If I live until the next year i will surely fast the 9th”
So it’s fasting is legislated, and Shaikh ul-Islaam sees that the fasting (the 9th) is Mustahab (recommended) in opposition to the people of the book.
Translated by Abu ‘Abdillah ‘Umar bin Yahya Al-‘Akawi