Is it valid to fast the day of 'Ashura alone?

The questioner : He says:The questioner : Is it valid to fast the day of 'Ashura alone, and what is the ruling for one who does so out of ignorance?

The Shaykh : Yes, it is valid to fast 'Ashura alone, and one is rewarded for it, because the Prophet (peace and blessings be upon him) said regarding the fasting of 'Ashura: However, some scholars disliked isolating it, meaning fasting only the tenth without fasting the day before or the day after. Some scholars disliked that, saying: "Because the last of the two commands from the Messenger of Allah (peace and blessings be upon him) was that he said:

the day before or the day after

خالفوا اليهود صوموا يوم قبله أو يوم بعده

Sunan Ibn Majah 1723Sahih (Darussalam)

And he said:

If I live till the next (year), I would definitely observe fast on the 9th

لئن بقيت إلى قابل لأصومن التاسع

Sahih Muslim 1134b

" Based on this, we say to the brother: fast a day before it or a day after it. Yes.