_Hāfiz Ibn Hajr (Rahimahullah):_
Fasting ʿĀshūrā is of three levels:
• The lowest is to fast it alone (10th Muharram).
• Above this is to fast the 9th along with it.
• Above that is to fast the 9th and the 11th along with it. And Allāh knows best (i.e., all three days 9th, 10th and 11th of Muharram).
[al-Fath, (4/246) | Hāfiz Ibn Hajr (Rahimahullah)]
There are three levels of fasting ʿĀshūrā.
The most complete is to fast a day before it and a day after it.
After this is to fast (only) the 9th and the 10th, and the majority of Aḥādīth (are found to support this).
Lastly, to fast the 10th by itself.
“`????[Ibn al-Qayyim (Rahimahullah) Zād al-Maʿād, Page: 72]”`