Who was the killer of Al-Hussain, may Allah be pleased with him?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

Al-Husayn ibn ‘Ali was killed during the reign of Yazeed ibn Mu‘aawiyah. ‘Ubaydullah ibn Ziyaad, ‘Amr ibn Sa‘d, and the likes of them played a major role in killing him.

Ath-Thahabi said in the biography of Yazeed, “He was a strong enemy to the family of the Household of the Prophet and he was a very rough and tough person. He used to drink alcohol and do evil. He started his reign with the killing of Al-Husayn, and he ended it with the Battle of Al-Harrah, so the people hated him.”

Ibn Al-‘Imaad said in Shadharaat Ath-Thahab, “Then ‘Ubaydullah ibn Ziyaad increased the army until they reached twenty-two thousand soldiers, and their commander was ‘Umar ibn Sa‘d ibn Abi Waqqaas. They agreed to kill him (Al-Husayn) on the day of ‘Aashooraa’...”

Ibn Abi Khaythamah said in his book At-Taareekh, “I heard Yahya ibn Ma‘een say, ‘‘Umar ibn Sa‘d ibn Abi Waqqaas is a Kufi (i.e. he lived in Kufah).’ I asked him, ‘Is he trustworthy?’ He replied, ‘How can the one who killed Al-Hussayn be trustworthy?’”

For more benefit, please refer to fatwas 84152 and 85186.

Allah knows best.