Islamic military jurisprudence refer to what has been accepted in Fiqh by ulema (Islamic scholars) as the correct Islamic manner which expected to be obeyed by Muslims, but it may differ with what has been done in Muslim history.
Jihad (Arabic for "struggle") was given a military dimension after the oppressive practices of the Meccan Quraish against Muslims. It was interpreted as the struggle in God's cause to be conducted by the Muslim community. Injunctions relating to jihad have been characterized as individual as well as collective duties of the Muslim community. Hence, the nature of attack is important in the interpretation — if the Muslim community as a whole is attacked jihad becomes incumbent on all Muslims. Jihad is differentiated further in respect to the requirements within Muslim-governed lands (Dar al-Islam) and non-Muslim lands (Dar al-Harb).
Military jurisprudence, over time, has been affected by other factors as well. Hamidullah lists the practices of early caliphs (revered as righteous), consensus amongst Muslim jurists (ijma) and norms established by treaties, pacts and conventions as sources for Islamic military law.
According to Shaheen Sardar Ali and Javaid Rehman, the Islamic military laws are in line with rules of modern international law, although not entirely synonymous. Ali and Rehman also reject the notion that Islamic laws fall short of modern standards and argue that Islamic legal principles can be applied to modern law to build a better order. They point to the dual commitment of Organisation of the Islamic Conference (OIC) member states (representing most of the Muslim world) to Islamic law and the United Nations Charter, as evidence of compatibility of both legal systems.
The basic principle in fighting in the Quran is that other communities should be treated as one's own. Fighting is justified for legitimate self-defense, to aid other Muslims and after a violation in the terms of a treaty, but should be stopped if these circumstances cease to exist. Although the language can be considered militant, the principle of forgiveness is reiterated in between the assertions of the right to self-defence.
During his life, Muhammad gave various injunctions to his forces and adopted practices toward the conduct of war. The most important of these were summarized by Muhammad's companion, Abu Bakr, in the form of ten rules for the Muslim army:
Stop, O people, that I may give you ten rules for your guidance in the battlefield. Do not commit treachery or deviate from the right path. You must not mutilate dead bodies. Neither kill a child, nor a woman, nor an aged man. Bring no harm to the trees, nor burn them with fire, especially those which are fruitful. Slay not any of the enemy's flock, save for your food. You are likely to pass by people who have devoted their lives to monastic services; leave them alone.
These injunctions were honored by the second Caliph, Umar, during whose reign (634–644) important Muslim conquests took place. These principles were also honoured during the Crusades, as exemplified by sultans such as Saladin and al-Kamil. For example, after al-Kamil defeated the Franks during the Crusades, Oliverus Scholasticus praised the Islamic laws of war, commenting on how al-Kamil supplied the defeated Frankish army with food:
In addition, during the Battle of Siffin, the Caliph Ali stated that Islam does not permit Muslims to stop the supply of water to their enemy. In addition to the Rashidun Caliphs, hadiths attributed to Muhammad himself suggest that he stated the following regarding the Muslim conquest of Egypt:
The early Islamic treatises on international law from the 9th century onwards covered the application of Islamic ethics, Islamic economic jurisprudence and Islamic military jurisprudence to international law, and were concerned with a number of modern international law topics, including the law of treaties; the treatment of diplomats, hostages, refugees and prisoners of war; the right of asylum; conduct on the battlefield; protection of women, children and non-combatant civilians; contracts across the lines of battle; the use of poisonous weapons; and devastation of enemy territory.
Traditionally, "adults" have been defined as post-pubescent individuals above the age of 15. Due to expediency during the Iran-Iraq war, however, Ruhollah Khomeini (Iran's then supreme political and Islamic leader) issued a fatwa lowering the age of the combatants as well as waiving the family's permission as a condition to enlist.
Muslims have struggled to differentiate between legitimate and illegitimate wars. Fighting in self-defense is not only legitimate but considered obligatory upon Muslims, according to the Qur'an. The Qur'an, however, says that should enemy hostile behavior cease, then the reason for engaging such enemy also lapses.
Some scholars argue that war may only be legitimate if Muslims have at least half the power of the enemy (and thus capable of winning it). Other Islamic scholars consider this command only for a particular time.
Javed Ahmad Ghamidi believes that after Muhammad and his companions, there is no concept in Islam obliging Muslims to wage war for propagation or implementation of Islam. The only valid basis for military jihad is to end oppression when all other measures have failed. Islam only allows jihad to be conducted by a government.
According to Abdulaziz Sachedina, offensive jihad raises questions about whether jihad is justifiable on moral grounds. He states that the Qur'an requires Muslims to establish just public order, increasing the influence of Islam, allowing public Islamic worship, through offensive measures. To this end, the Quranic verses revealed in the latter part of Muhammad's career require Muslims to wage jihad against unbelievers. This has been complicated by the early Muslim wars of expansion, which he argues were although considered jihad by Sunni scholars, but under close scrutiny can be determined to be political. Moreover, the offensive jihad points more to the complex relationship with the "People of the book" than their conversion.
Sunni jurists believe that jihad can be declared by a political leader with the sanction of religious Islamic authorities. The Shia jurists, however, hold that only a just spiritual leader can declare jihad and ensure that it is conducted in accordance with the principles of justice. Historically, the lack of a central religious authority has created problems with the general acceptance of these declarations. Rulers and other individuals have on occasion declared jihad even when Islamic clerics have refused to categorize the conflict as such. An example of such a declaration was made by the Ottoman Sultan during World War I.
According to professor Sayyid Dāmād, no explicit injunctions against use of chemical or biological warfare were developed by medieval Islamic jurists as these threats were not recognized. However, Khalil al-Maliki's Book on jihad states that combatants are forbidden to employ weapons that cause unnecessary injury to the enemy, except under dire circumstances. The book, as an example, forbids the use of poisonous spears, since it inflicts unnecessary pain.
Harming civilian areas and pillaging residential areas is also forbidden, as is the destruction of trees, crops, livestock and farmlands. The Muslim forces may not loot travellers, as doing so is contrary to the spirit of jihad. Nor do they have the right to use the local facilities of the native people without their consent. If such a consent is obtained, the Muslim army is still under the obligation to compensate the people financially for the use of such facilities. However, Islamic law allows the confiscation of military equipment and supplies captured from the camps and military headquarters of the combatant armies.
Islamic jurisprudence calls for third party interventions as another means of ending conflicts. Such interventions are to establish mediation between the two parties to achieve a just resolution of the dispute.
If, however, non-Muslims commit acts of aggression, Muslims are free to retaliate, though in a manner that is equal to the original transgression. The "sword verse", which has attracted attention, is directed against a particular group who violate the terms of peace and commit aggression (but excepts those who observe the treaty). Crone states that this verse seems to be based on the same above-mentioned rules. Here also it is stressed that one must stop when they do. Ibn Kathir states that the verse implies a hasty mission of besieging and gathering intelligence about the enemy, resulting in either death or repentance by the enemy. Crone continues that there is only one verse in the Qur'an which seems to endorse war of aggression. However, if read as a continuation of previous verses, it would be concerned with the same oath-breaking of "polytheists".
The legal principles governing the treatment of prisoners of war are outlined in the Islamic law (in the traditional schools of Islamic jurisprudence). These principles closely mirror the pre-Islamic norms of society during Muhammad's time.
Men, women, and children may all be taken as prisoners of war under traditional interpretations of Islamic law. Generally, a prisoner of war could be, at the discretion of the military leader, freed, ransomed, exchanged for Muslim prisoners, or kept as slaves. In earlier times, the ransom sometimes took an educational dimension, where a literate prisoner of war could secure his or her freedom by teaching ten Muslims to read and write. Some Muslim scholars hold that a prisoner may not be ransomed for gold or silver, but may be exchanged for Muslim prisoners.
Women and children prisoners of war cannot be killed under any circumstances, regardless of their religious convictions, but they may be freed or ransomed. Women who are neither freed nor ransomed by their people were to be kept in bondage and referred to as ma malakat aymanukum. Islamic law does not put an exact limit on the number that can be kept in bondage. It strictly forbids keeping female slaves as a means of sexual enjoyment and luxury according to the Islamic scholar Maududi.
During their first civil war, Muslims fought at the Battle of Bassorah. In this engagement, Ali (the caliph), set the precedent for war against other Muslims, which accepted by most later Muslims. According to Ali's rules wounded or captured enemies should not be killed, those throwing away their arms should not be fought, and those fleeing from the battleground should not be pursued. Only captured weapons and animals (horses and camels which have been used in the war) are to be considered war booty. No war prisoners, women or children are to be enslaved and the property of the slain enemies are to go their legal Muslim heirs.
Different views regarding armed rebellion have prevailed in the Muslim world at different times. During the first three centuries of Muslim history, jurists held that a political rebel may not be executed nor his/her property confiscated.
Classical jurists, however, laid down severe penalties for rebels who use "stealth attacks" and "spread terror". In this category, Muslim jurists included abductions, poisoning of water wells, arson, attacks against wayfarers and travellers, assaults under the cover of night and rape. The punishment for such crimes were severe, including death, regardless of the political convictions and religion of the perpetrator. Further, rebels who committed acts of terrorism were granted no quarter.