For Sunni Muslims, Ashura marks the parting of the Red Sea by Moses and the salvation of the Israelites. Ashura is celebrated in Sunni Islam through supererogatory fasting and other acceptable expressions of joy.

By contrast, for Shia Muslims, Ashura is a day of mourning as they annually commemorate the death of Husayn ibn Ali, grandson of the Islamic prophet Muhammad and the third Shia imam.

Do you fast, mourn or not do anything? For those who accept hadiths of course.