Ali had willed that his assassin should not be subjected to any torture but should be killed with one stroke of the sword. The assassin was a fanatic, and instead of being remorseful at his ghastly deed and heinous crime he continued to boast of his services to Islam in assassinating Ali. That annoyed the Muslims, and contrary to the will of Ali his assassin was subjected to torture. His eyes were seared, and his limbs were cut off. Thereafter his dead body was put in a sack and burnt.
"When a person dies, his works end, except for three: ongoing charity, knowledge that is benefited from, and a righteous child who prays for him."
Prophet Mohammed (PBUH)
"The best of what a man leaves behind are three: a righteous child who supplicates for him, ongoing charity the reward of which reaches him, and knowledge that is acted upon after him."
Sunan Ibn Mājah
"Every day two angels come down from Heaven and one of them says, 'O Allah! Compensate every person who spends in Your Cause,' and the other (angel) says, 'O Allah! Destroy every miser.'"
Sahih Bukhari