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 event of Karbala when Imam al-Husayn (a) and his companions were martyred on the day of Ashura, (10th of Muharram 61 AH/13th of October 680.) It is reported that the captives of the Event of Karbala came to visit Imam al-Husayn (a) in Karbala on 20th of Safar 61 AH (November 22, 680) on their return from Syria to Medina. In a hadith from Imam al-Hasan al-'Askari (a), Ziyara of Arba'in is considered among the sings of the faithful. This day is a national holiday in Iran. Shi'a mourn on the day of Arba'in and mourning groups rally in streets. Great procession of Shi'a who try to arrive in Karbala on the day of Arba'in is one of the most important mourning ceremonies of Shi'a around the world. Procession of Arba'in is regarded as an act of following the mentioned hadith.