Arba'in of Imam al-Husayn (a)
Arbaʿīn of Imam al-Ḥusayn (a) (Arabic: اربعين الحسیني) is 20th day of Safar in the Hijri Lunar calendar and the anniversary of the 40th day after the Battle of Karbala when Imam al-Husayn (a) and his companions were martyred on the Day of Ashura, (Muharram 10, 61 AH/October 10, 680). It is reported that the Captives of the Battle of Karbala came to visit Imam al-Husayn (a) in Karbala on Safar 20, 61/November 19, 680) on their return from Syria to Medina.
This day is a national holiday in Iran. Shi'a mourn on the day of Arba'in and mourning groups rally in streets. In recent years, great procession of Shi'a who try to arrive in Karbala on the day of Arba'in has become one of the most important mourning ceremonies of Shi'a around the world and it has even turned into one of the largest religious processions on a global scale . Currently the majority of foreign pilgrims in this procession are from Iran.