What is "tatbir"

Tatbir , also known as Talwar zani and Qama Zani in South Asia, is an act of mourning by some of Shia Muslims for the younger grandson of Muhammad, Husayn ibn Ali, who was killed along with his children, companions and near relatives at the Battle of Karbala by the Umayyad Caliph Yazid I. Tatbir is a contested issue among Shia clerics. Some clerics deem it to be self-damage and hence Haram, while traditionalist clerics allow believers to indulge in Tatbir.