Islām’s Prohibition of Taking Lives Unjustly and Causing Fear in the Earth
From the Tafsīr of al-Allāmah ‘Abd al-Raḥmān ibn Nāṣir al-Sa’dī
Translated by Abū al-Ḥasan Mālik Ādam al-Akhḍar

Relating the story of the Prophet Mūsā (alaihissalam), Allāh (Subhanahu wa ta'aala) says in His Noble Book:
“And he entered the city at a time of inattention by its people and found therein two men fighting: one from his faction and one from among his enemy. And the one from his faction called for help to him against the one from his enemy, so Mūsā struck him and [unintentionally] killed him. [Mūsā] said, ‘This is from the work of Satan. Indeed, he is a manifest, misleading enemy.’He said, ‘My Lord, indeed I have wronged myself, so forgive me,’ and He forgave him. Indeed, He is the Forgiving, the Merciful.’” [al-Qaṣaṣ 28:15-16]

Until the verse:

“And when he wanted to strike the one who was an enemy to both of them, he said, ‘O Mūsā, do you intend to kill me as you killed someone yesterday? You only want to be a tyrant in the land and do not want to be of the amenders.’” [al-Qaṣaṣ 28:19]
In his Tafsīr [commentary] of these verses, al-Allāmah ‘Abd al-Raḥmān ibn Nāṣir al-Sa’dī (rahimahullaah) says:

“And from them (i.e. the benefits of these verses): The killing of a non-Muslim who has a compact [of security] by treaty or customary law is impermissible,[1] for indeed Mūsā(alaihissalam) considered his killing of the disbelieving Copt a sin, and he sought Allāh's (Subhanahu wa ta'aala) Forgiveness for it.
Also from them: Whoever takes a life unjustly is considered from the oppressors, those who cause corruption in the earth.
And from them: Whoever takes a life unjustly and claims that he desires to rectify the land and to cause fear in the people of sin, then he is indeed a liar in this [claim] and is instead one who causes corruption, just as Allah (Subhanahu wa ta'aala) has related in the Copt’s statement (You only want to be a tyrant in the land and do not want to be of the amenders) by way of affirmation, not negation.”[2]

References:

[1] This has also been explicitly stated by the Messenger of Allāh (sallallaahu alaihi wa sa in the ḥadīth collected by Imām al-Bukhārī in his Ṣaḥiḥ (no. 2929 and 6524) on the authority of ‘Abd Allāh ibn ‘Amr (radhi Allaahu anhu) who related that Allāh’s Messenger (Sallallaahu alaihi assalam) said: “Whoever killed a Mu'ahid (a non-Muslim who is under the pledge of protection by the Muslims) will not smell the fragrance of Paradise though its fragrance can be smelled at a distance of forty years (of traveling).”
[2] Taysīr al-Karīm al-Raḥmān (pg. 678)


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