Tasu’a, also spelled Tassoua, is observed on the ninth day of Muharram, which falls every year before Ashura, an important Islamic holiday. It is primarily celebrated in Iran, where it is recognized as a public holiday, while Ashura is observed in several countries with significant Shia populations, including Afghanistan, Iraq, and Lebanon. Tasu’a commemorates events related to the Battle of Karbala and the martyrdom of Imam Husayn ibn Ali, focusing particularly on the loyalty of Abbas ibn Ali, Husayn's half-brother and standard-bearer. On this day, Shia Muslims participate in public mourning ceremonies, attend mosques, recite Hadith, and read poems in honor of Abbas. Other customs include chanting, processions, self-flagellation, and Ta’zieh, which are religious plays depicting the events of Karbala. The Al-Abba Shrine in Iraq, where Abbas is buried, is a notable location associated with Tasu’a.