What is "hurmala"

In Islamic History, Hurmala Ibn Kahil Al Asadi Alkoofi was the killer of Ali al-Asghar ibn Husayn, the Imam Hussain's child, and the great-grandchild of Muhammad, on 10 October, 61 AH (680 CE).

When the Imam had lost all hope in the enemy in the Battle of Karbala, he came out riding on a horse and asked for water for his six-month-old child who was dying of thirst. Omar gave the order and Hurmala sent a three-headed arrow flying into the little child's neck.

He was later captured and killed by the forces of Mukhtar al-Thaqafi.