From his blog:
Peace and Justice in Islam
from Notes: New Islamic Directions by Imam Zaid
We are living in a world where there could obviously be more peace. As Muslims, we realize this fact more than most people, as the peace of many of our brothers and sisters in various parts of the globe has been tragically disrupted –in Palestine, Iraq, Afghanistan, Somalia, and other locales. Similarly, we are living in a world where there could be more justice. We read almost daily of assassinations in various parts of the world, where terrorist groups, military forces or intelligence services, oftentimes in summary fashion, declare victims guilty, and then proceed to execute them. Unfortunately, such unprincipled political behavior has become increasingly common in both the foreign and domestic policies of this country, causing untold damage to her image and credibility abroad.
These two issues, peace and justice, are joined in the slogans we hear from many activists, especially here in the United States, “No Justice, No Peace!”  This linkage is logical, as justice must be considered one of the indispensable prerequisites of any lasting peace. This article intends to briefly look at the ideas of peace and justice in Islam and explore their deeper significance in the life of a Muslim.
In the Arabic language, the word peace is derived from the radicals S-L-M. The scholars of language mention four closely related terms that can be derived from this origin: Salaam, Salaamah, Silm, and Salm. Raghib al-Isfahani says in his lexicon of Qur’anic terms, “Al-Salm and al-Salaamah mean freedom from any external or internal ruination.”  Based on that he mentions that true peace will only exist in Paradise, for only there will there be perpetuity with no end; complete satisfaction with no need; perfect honor with no humiliation; and perfect health with no disease. In this regard, God is known as al-Salaam, because He alone is described as being totally free from any defects or flaws.  This understanding of peace being, ultimately, a reality associated with a transformed world, is also understood in both Jewish and Christian theology. 
At the level of interstate relations, if we ponder the above definition, we can consider peaceful relations between nations as a condition where violence, a state inevitably involving both internal and external ruination, is absent. In this sense, war can be viewed as an aberrational state. The aberrational nature of war is made clearer if we consider that murder, the ultimate consequence of war, is considered an innovation, which destroyed the peace formerly existing among the human family. It is stated in a prophetic tradition, “No soul is killed unjustly, except that the elder son of Adam [Cain] shares in the stain of the crime. That is because he was the first to innovate murder [in the human family].” 
At the individual level, peace can be viewed as an absence of the ruinations of the heart. One free from such ruinations, will succeed, God-willing, when he/she meets his/her Lord. Therefore, he/she will enter safely into the Abode of Peace [Dar as-Salaam]. God says in that regard, Dar as-Salaam], and there he/she will know true peace.
Peace does have meanings wider than those mentioned above. One of the loftier objectives of our religious is to introduce into the world an ethos that facilitates the spreading of peace at every level. Our personal relations with our fellow Muslims should begin with the implementation of the Prophetic order, “Spread peace between you all.”  This order is so pressing that the Beloved Prophet, peace and blessings of God be upon Him, advised its indiscriminate implementation. He says at the end of a tradition in which he described one of the best forms of Islam, “Extent the greeting of peace, to those you know and those you know not.”  This is a very weighty matter, which calls for our deeper reflection. Its weightiness is illustrated by the fact that it is mentioned as being one of the things that completes our faith. The Prophet, peace and blessing of God upon Him, said in that regard, “You will not enter Paradise until you believe, and you will not believe until you love one another. Shall I indicate to you something that will surely lead to your mutual love? Spread the greeting and spirit of peace between yourselves.” 
Our relations with our spouses should also be characterized by peace. God admonishes us concerning those relations, “And peace is best.” [4:128] Similarly, in our relations with other nations, God commands us, If they [the enemy] inclines towards peace, then you should similarly incline, and place your trust in God. [8:61] As mentioned above, peace is the original state that prevailed in relations between individuals and societies. This opinion is based, among other narrations, on the saying of the Prophet, peace and blessings of God be upon Him, that Jesus, peace be upon him, “will return the world to a state of peace” [Yurji’ as-Salaam] after his appearance at the end of time. 
As we have explained above, the original state in human affairs is peace. One of the principles operative in our law is that we do not move away from the original ruling in any affair without a valid justification. Corporate greed and imperial hubris do not constitute legitimate justifications in this regard. This principle, coupled with the imperative of preserving innocent life, makes it imperative that we work to avoid war. The imperative to preserve innocent human life arises from the verse, Whoever saves an innocent life it is as if he has saved all of humanity, and whoever takes a life unjustly, it is as if he has murdered all of humanity. (Qur’an 5:32)
Our lexicographers define justice, variously, as, “To rule based on that contained in the Book of God and the tradition [Sunnah] of His Messenger, peace and blessings of God upon Him, and refraining from ruling based on empty opinion.” It is also defined as “extending inherent rights [to their possessors] equitably.”  This latter definition emphasizes the importance of equity as an essential aspect of distributive justice.
The concept of justice is one of the essential pillars in the maintenance of both the natural and social orders. God, be He Exalted, has said, …and He has established the scale, therefore, do not transgress in the scale [of justice]. Undertake the measuring with justice and do not cheat concerning the scale. [55:7-8] Justice, as many of our scholars point out, is one of the underpinnings of the order that has been established by God. This reality is also a foundation of a healthy social order. God says in that regard, O, You who believe! Be upright for God, witnesses to justice; and do not let your hatred of a people move you to a position where you are unjust. Be just, that is closer to piety. Be mindful of God! Verily God is well-informed concerning all that you do. [4:135]
This social aspect of justice has been beautifully summarized by Imam al-Qurtubi. He says, discussing the relationship between two words which are usually translated as justice [al-‘Adl], and distributive justice [al-Qist] “Justice is the basis of all human relations and a foundation of Islamic rule.”  This saying is illustrative of the meaning conveyed by the saying of God, Verily, We have sent Our Messengers with clear proofs, and We have revealed unto them the Scripture and the Balance in order that they lead people with Justice… [57:25]
Imam Mawardi has summarized the social implications of distributive justice in the following way:
One of the things that reforms worldly affairs is the principle of distributive justice. It facilitates amicable relations between people, engenders obedience to the Divine Law, and brings about the prosperity of countries. It is the basis of a thriving economy, strong families, and stable government. Nothing devastates the land nor corrupts the mind as quickly as tyranny. That is because there are no acceptable limits [to regulate tyranny]. 
For this reason, Ibn Taymiyya sees the responsibilities of Islamic government emanating from a single verse in the Qur’an, God enjoins that you deliver the Trusts to their rightful possessors. And when you rule over [or judge between] people, that you do so with justice… [4: 58]  The Noble Prophet, peace and blessings of God be upon Him, has said in this context, “Surely the most beloved of people with God, and the closest to Him on the Day of Resurrection will be a just leader. And the most hated of people and the furthest removed from Him will be a tyrannical leader.” 
Clearing himself from even an inadvertent association with oppressive, unjust acts, our beloved Prophet, peace and blessings of Allah be upon Him, is reported to have said, “You bring your disputes to me for adjudication; perhaps one of you is less eloquent than another, and I rule against the wronged party on the basis of what I have heard. Therefore, if I inadvertently grant one of you something owed to his brother do not take it, for I am granting him something that constitutes a piece of Hellfire.” 
Our impeccably just Khalifa, Umar Ibn al_Khattab, relates the following penetrating words:
Verily, God sets forth parables for you, and He directs admonition towards you in order that hearts will be quickened. Surely, the hearts are dead until God quickens them. Justice has signs and portents. As for its signs, they are shyness, generosity, humility, and gentleness. As for its portents, they are embodied in mercy. He has [likewise] made for every affair a gate, and He has made that gate accessible by providing a key. The gate of justice is a deep consideration of consequences, and its key is otherworldliness. Consideration of consequences ultimately involves remembering death, and preparing for it by freely parting from one’s wealth. Otherworldliness involves dealing justly with everyone and being satisfied with what suffices. If one is not satisfied with what suffices him, no abundance will every enrich him.” 
Much of this discussion has focused on distributive justice. However, the Qur’an also places great emphasis on commutative justice. God commands in Sura an-Nur, Do not be moved by partiality to discriminate in meting out divinely legislated punishments. [24:2] The Prophet Muhammad, peace and blessings of God be upon him, mentioned that one of the reasons behind the ruination of a nation is a lack of commutative justice.  In this context, he mentioned that if his very daughter were to steal, he would not hesitate to punish her to the full extent of the law. 
In summary, this brief discussion should make it clear to any fair-minded person that peace and justice are comprehensive concepts with deep implications. To be true to our appellation, Muslim, we have to be people committed to peace and justice. We must clearly illustrate to the world that our religion is indeed the religion of peace. However, our striving for peace must never allow us to be unjust, nor should it allow us to passively accept injustices.
We must take a stand for justice, as we are ordered in the Qur’an, Be you upright supporters of justice… [4: 135] However, that stand must go far beyond slogans, such as the one mentioned at the beginning of this article, and move into the realm of positive action. Action inspired by the Qur’an, and the words and deeds of our illustrious Prophet, peace and blessings of God upon him. These twin sources served as the basis for the just words and actions of our righteous forebears, some of which have been mentioned in this article.
This slogan has been particularly popularized by the New York –based activist, Rev. Al Sharpton, and his followers.
Raghib al-Isfahani, al-Mufradat fi Gharib al-Qur’an (Beirut:Dar al-Ma’rifa, no date), 239.
Al-Mufradat, p. 239.
See The Holy Bible, Isaiah, 9:6-7; and John 14:27.
Ibn Hajar al-‘Asqalani, Fath al-Bari Sharh Sahih al-Bukhari (Damascus: Dar al-Fayha’, 1417/1997), 13:369, no. 7321.
This Hadith is related by Imam Muslim, Imam Abu Dawud, and Imamal-Tirmidhi in their collections. Quoted in Abi Zakariyya Yahya ibn Sharaf al-Nawawi, Riyad al-Salihin, (Damascus: Dar al-Ma’moun Li al-Turath, 1994) 289-290.
 Ibn Hajar al-‘Asqalani, Fath al-Bari (Damascus: Dar al-Fayha’, 1997), 11: 26-27. The full text of the Prophetic Tradition follows: A man asked the Prophet (Peace and Blessings of Allah be upon) “Which Islam is best?” He replied, “That you provide food, and extend the greeting of peace, to those you know and those you know not.”
 This is the full narration of the Prophetic Tradition mentioned in note no.4 above.
 Prophetic traditions, which narrate this meaning are related by Imam al-Bukhari, Imam Muslim, and Imam Ibn Majah. See for example, Fath al-Bari, 6:599-600. The above quote is from the version of Ibn Majah. Imam al-Bukhari’s version mentions that Jesus will “…put an end to war.”
 These and other definitions of justice are mentioned in Salih ibn ‘Abdullah ibn Humayd, Nadr al-Na’im fi Makarim Akhlaq al-Rasul al-Karim (Jeddah: Dar al-Wasila, 2000) 7: 2792.
 Quoted in Nadr al-Na’im, 8:3153.
 Quoted in Nadr al-Na’im, 7:2793.
 See Ahmad ibn Taymiyya, Al-Siyasa Al-Shar’iyya (Beirut: Dar al-Afaq al-Jadida, 1983) 4-5.
 Abu ‘Isa al-Tirmidhi, al-Jami’ (Cairo: Dar Ihya al-Turath al-‘Arabi, 1938), no. 1329.
 Fath al-Bari, 5:354.
 Quoted in Nadr al-Na’im, 7:2811.
 This concept is mention at the beginning of the tradition where a lady from Bani Makhzum, one of the most aristocratic Arab tribes, stole something and the companions were moved to intervene for a lessening of her punishment. The Noble Prophet, peace and blessings of Allah be upon him, responded, “O people! Those before you were ruined in that if a noble person among them stole something, they left him alone. On the other hand, if a lower class person stole something, they punished him!” See this narration in its entirety in Abi Zakariyya Yahya ibn Sharaf al-Nawawi, al-Minhaj: Sharh Sahih Muslim (Beirut: Dar al-Ma’rifa, 1419/1998), 11:186-187, no. 4386.
 Al-Minhaj, 11:186-187, no. 4386.