Spiritual Disease and Its Cure by Imam Shams-ud-Deen Muhammad bin Abi Bakr bin Qayyim AlJ awziyyah

Tyranny and oppression are among the greatest sins because they oppose justice, upon which the heavens and the earth were established. Allah ~ sent His Messengers and Books in order that people might establish justice among themselves. The act of killing unlawfully, without any right, is a great sin. Islam cites many examples of such evil acts, like the killing of one's child for fear that the child might share one's provision (i.e. food, drink, and money); the killing of one's parents who were the cause of one's existence; the killing of one's kin. The grade of such an evil act differs according to the nature of the act itself; therefore, the person who will receive the utmost punishment on the Day of Resurrection is the one who killed a prophet, followed by the one who killed an Imam, or a scholar who commanded justice among people and invited them to the Path of Allah ~- Allah ~ has set the punishment for the intentional killing of a believer as dwelling eternally in the Hell-Fire, with the Curse and Anger of the Lord.