Amina Inloes, Amina Inloes is originally from the US and has a PhD in Islamic Studies from the University of Exeter on Shi'a hadith. She is the program leader for the MA Islamic Studies program at the... Answered 1 year ago

Sh'is do not accept the hadith saying to fast on Ashura as valid. They are considered fabrications which came about in/after the time of Yazid to promote Ashura as a day of celebration. (Indeed, in some areas, Ashura is still celebrated as a holiday.)

For more information, you can look at resources such as this: https://www.al-islam.org/understanding-karbala-allamah-sayyid-saeed-akhtar-rizvi/appendix-4-fasting-ashura