God commanded the Muslims to be just at all time, even if it’s against their own selves and families.
4:135 O you who believe, stand with justice as witnesses to God, even if against yourselves, or the parents or the relatives. Even if he be rich or poor, God is more worthy of them, so do not follow desire into being unjust. And if you twist or turn away, then God is Expert over what you do.
5:8 O you who believe, stand for God and be witnesses for justice, and let not the hatred towards a people make you avoid being just. Be just, for it is closer to righteousness, and be aware of God. God is expert over what you do.
This “Islamic Justice” can and does apply today for both Muslims and non-Muslims living under the Islamic Law, where if a Muslim kills a non-Muslim, then his punishment would be the same as the punishment of killing a Muslim.
No where in the Quran do we find a direct punishment to a Muslim who intentionally kills a non-Muslim. However, it is important to know why no such law exists.
When the Quran was revealed 1400 years ago, it was revealed during times of hostile wars. The Muslims fought Pagan Arab tribes and the tribes of the Jews and Christians as well. Fighting the offending disbelievers was part of the Muslims’ routine in dealing with the disbelievers.
Despite all of this hostility between the Muslims and the Pagans and the Jews and Christians, God in the Quran prohibited for the Muslims to violate anyone who wanted peace:
2:190 And fight in the cause of God against those who fight you, but do not aggress, God does not love the aggressors.
Fighting in the cause of God those who fight us is what “Jihad” is all about. I can’t go and kill a non-Muslim just because he is a non-Muslim. That is absolutely forbidden in Islam.
Now, it is important to know that the Muslims never had an “Islamic State” or “Islamic Country” while the Quran was revealed. There was never a “Muslim Nation” during Prophet Muhammad’s time. But however, God did recognize the existence of nations:
49:13 O people, We created you from a male and female, and We made you into nations and tribes, that you may know one another. Surely, the most honorable among you in the sight of God is the most righteous. God is Knowledgeable, Expert.
Today, people are entirely divided into countries and nations. There isn’t any land on earth that isn’t under a government’s rulership. All national citizens’ lives in any nation are equal, except with those who oppose the dictators and end up getting killed by them. But the general equality between normal citizens exists today and had existed 1400 years ago when the Verse 49:13 was revealed.
So, what did God say about the citizens of any nation? Let us look at the following Verses about the story of Abel and Cain, Adam’s sons in the Noble Quran:
5:27-32 And recite to them the news of the two sons of Adam with truth. They had both made an offering, and it was accepted from one of them, and not accepted from the other. He said: “I will kill you!” He said: “God only accepts from the righteous.” “If you stretch your hand to kill me, I will not stretch my hand to kill you, for I fear God, Lord of the worlds.” “I want you to have both my sin and your own sin, and you will then be among the dwellers of the Fire. Such is the recompense of the wicked.” So he found it in himself to kill his brother; so he killed him. He thus became one of the losers. So God sent forth a raven to scratch the land and show him how to deal with the body of his brother. He said: “Woe to me! Am I not even able to be like this raven and deal with the body of my brother?” So he became of those who regretted. It is because of this that We have decreed for the Children of Israel: “Anyone who kills a person for other than murder, or Rebellion in the land; then it is as if he has killed all the people! And whoever spares a life, then it is as if he has given life to all the people.” Our messengers had come to them with clarities, but many of them are, after this, still corrupting on the earth.
As we clearly above in the above Verses 5:32 and 2:190, God prohibits the killing of any innocent person. There are other Verses where God commands the Muslims to honor any peace treaty they make with the enemy in the time of war and to never break it: Verses 4:90 and 9:7.
So if there are several instances in the Quran where God clearly prohibits the killing of any innocent non-Muslim, then violating God’s laws would result the offending Muslim in a sever consequence in the Day of Judgment.
But what about the judgment in life? I believe that since God clearly said “Anyone who kills a person for other than murder, or Rebellion in the land; then it is as if he has killed all the people!”, then this Verse is referring to all of the people living in the country, hence, treating all citizens equally.
As I said, since no Islamic government and no Islamic nation really existed during Prophet Muhammad’s time 1400 years ago, then the idea of treating all citizens (Muslims and non-Muslims) equally under one country’s law, and executing anyone who kills anyone intentionally would definitely be a supported in Islam. If killing any innocent person is equivalent to killing everyone as clearly mentioned in Verse 5:32 above, then it would definitely be appropriate to apply the conditions that are applied as shown above in the verse mentioned in the post for killing of any believer by a believer.