Tasoua Hosseini is a significant religious holiday observed in Iran. The occasion happens during Muharram, the first month of the Islamic calendar, more specifically on the ninth day. This holiday primarily commemorates the martyrdom of Imam Hussein, the grandson of Prophet Muhammad, and other members of his family and followers during the battle of Karbala.

On the eve of Tasoua Hosseini, Iranian people dress in black and participate in public processions and ceremonies. The mourners express their grief and sorrow through various acts such as chest beating (sinazani) and reciting sad poems (marthiyeh) to show their deep connection with Imam Hussein and his sufferings. Iranians also set up 'Sabil', which are stalls offering free food and drink as acts of charity, honouring Imam Hussein's characteristics of kindness and generosity.

Tasoua Hosseini is not only a religious but also a social event, underlining the values of self-sacrifice, resistance against injustice, and fighting for the righteous cause. These values are embodied by Imam Hussein’s heroic stand in the face of a much larger enemy. Despite its solemn nature, the holiday continues to bring together the Iranian people, in remembrance and reverence, year after year.