Battle of Karbala

Muslims and people of other community mourn for Hazrat Imam Husain (pbuh) in the month of Muharram. He, his family members, and his frinds and disciples were brutally killed by the forces of Ibn Ziyad. The mourning period is two months and eight days. First month is Muharram and second is Safar and both of them can be of either 29 or 30 days as they are lunar months. Eight days belongs to the month of Rab-al-Awwal