Tasua is the ninth day of Muharram and the day before Ashura. Several events took place on this day, including: the entry of the Shemra into Karbala, the provision of safe passage for the children of Umm-ul-Banin, preparations for war; and Hussein ibn Ali and his comrades were besieged by the enemy (as part of the Battle of Karbala). This day is attributed to Abbas ibn Ali due to his actions as the commander of Husayn ibn Ali's army.
Tasua is literally a variant of the Arabic word for "ninth" and refers to the ninth day of Muharram in the Islamic calendar.
On the days of Tesua and Ashura, Shia Muslims go to mosques and such or participate in mourning ceremonies. They recite hadiths and verses in honor of Abbas ibn Ali. In general, mourning ceremonies consist of processions, singing and self-flagellation. One of the oldest and most widespread traditions among Muslims is to wish for something from Allah while promising to feed the people.
In Iran, this tradition is well known and reaches its climax in Tasua and Ashura (9th and 10th of Muharram) when the mourners are fed. Ta'zieh as a religious play is an old traditional mourning practice in some towns and villages. Participants view Ta'zieh as part of a ritual mourning, rather than a typical play in which the actors must memorize their scripts. In other words, the actors read from the script.
Iran National and Public Holidays