This is an excerpt from The Muslim Conduct of State by Dr. Muhammad Hamidullah

(2) In other words, International Law means rules of the conduct of states in their mutual dealings. Obviously, it is not necessary that there should be only one set of rules, or one system of international law at a time, for the conduct of all the states of the world. And several systems of international law could, and in fact did, exist simultaneously in different parts of the globe. Even the modern, so-called European, International law is not a collection of unanimously approved rules.

(3) Islam has elaborated its own system of public international law. Before describing it in detail, it might be useful to define precisely what I mean by the term Muslim International Law. It is to note by the way, that throughout this book I have used "Muslim Law," "Islamic Law," "Shar'iah and Fiqh" as synonymous terms.

(4) Muslim International Law may be defined as: That part of the law and custom of the land and treaty obligations which a Muslim de facto or de jure state observes in its dealings with other de facto or de jure states.

(5) A few words of explanation may not he out of place.

(6) We have emphasised the point that what a Muslim State accepts as such is the Muslim International Law. This must be borne in mind from the very outset. Muslim International Law depends wholly and solely upon the will of the Muslim State, which in its turn is controlled by the Muslim Law (Shar'iah). It derives its authority just as any other Muslim Law of the land. 

Even the obligations imposed by bilateral or multilateral (international) treaties have the same basis; and unless they are ratified and executed by the contracting Muslim party, they are not binding; and their non-observance does not create any liability against the Muslim State. Of course it does not matter whether the acceptance is express or tacit.  It may be added that the promulgation and execution of International Law with the consent of all the States of the world is as ideal which has never been achieved, even for a short term, in the long annals of Man.

(7) We have, however, recognised in our definition that not only laws and customs of the land, but even treaties impose obligations upon a Muslim State. Treaties will be dealt with later; but what is law ?

(8) Law (Fiqh) is variously defined by classical Muslim jurisconsults. "The knowledge of what is for and upon one" is a definition attributed to Abu HanIfah) which in other words may be rendered as "the science of the rights and obligations of man". A late authority, Muhibbullah al-Bihariy, introduces this all-embracing subject in the following words  of his book (compiled 1109 H.) : " The science of ascertaining religious commands (regarding practical affairs of life) by means of their detailed guides." [By guides he means authority or source of information.]

(9) A glance at the contents of works on Fiqh would reveal that they embrace practically all the affairs of human' life, material as well as spiritual. In view of the standard definitions given above and is the face of the contents of works do Fiqh, there remains not the slightest doubt that international law, i.e. the rules of State-conduct in times of war, peace and neutrality, form part of the ordinary law of the land, the Fiqh. These rules of conduct are generally dealt with in books on Fiqh under the heading Siyar i.e. conduct, as we shall show in the next chapter.

(10) Here a brief expose of the origin of law according to Muslim jurists may profitably be added. They say that man must always do what is good, and abstain from what is evil, and take scrupulous care of the intermediary grades of plausible, permissible and disliked It is, however, not easy to distinguish between good and evil, especially when the matter concerns the subtleties of a complex civilised life beyond the pale of ordinary commonplace things. 

Practical needs would have required the possession of the power to legislate (or lay down definitely grades of good and evil [in] each and every matter) in the hands of Man, either individual, as jurisconsult, or collectively organised, i.e. a State. Yet mere reason, regarded as the touchstone of good and evil, is not without grave difficulties. For it is possible, and also a matter of fact -- so argue Muslim jurists -- that different persons opine differently regarding the same things. 

The belief in Messengers of God is useful even from the point of view of jurisprudence, in so far as the awe and respect due to their persons lead to the acceptance of certain fundamentals without further dispute, wherefrom other and further details may be elaborated. For this reason, the Muslim savants are very thankful to the generosity of God that He gave men along with reason certain chosen human Guldes to help them in the conduct of life. These selected and chosen ones pointed out what God commanded, God the real Sovereign and Lawgiver, regarding good and evil. Muhammad has been acknowledged by the Muslims as the Messenger of God; and whatever he gave them in his lifetime, commands as well as injunctions, in the name of his Sender, God, was accepted by the Muslims as indisputably final and most reasonable. 

These Divine Commands, known as the Qur'an and the Hadith - as we shall see later in detail - served practically all the needs of the Muslim community of that time. But human needs multiplied later in such a manner that express provision seemed to be available for some of  the new matters in either the word or deed of the Messenger, who himself had passed away, disconnecting the link whereby Man could receive Commands from his Lord. The consequent result would have been fatal and the fabric of Fiqh would soon have collapsed under the strain, had not there been express provision in the law itself for further elaboration. Credit must also not fail to be given to the Muslim jurists, after the death of the Prophet, who not only discerned this elasticity of the Divine Law, but also utilized it to its fullest extent. In time there emerged a complete system of law which served all the purposes of the Imperial Muslims, even at the height of their widest expansion from the Atlantic to the Pacific Oceans.

(11) Thus law originated from the direct Commands of God; but the power retained by man to interpret and expand Divine Commands, by means of analogical deductions, and other processes, provided all that was required by the Muslims. In this way a dual need was served: that of sanctity to inspire awe in the minds of (hose who were intended to observe it, and that of elasticity or capability of development to meet the needs of times and circumstances.

(12) We have defined international law, first, as a part of the law of the land. The province of the law of the land is therefore, obviously, wider than that of international law; and we have no concern here with the portion of the law of the land which regulates internal affairs of the State or its subjects.

(13) We have also acknowledged customs as contributing to international law. No system of law can positively provide guidance regarding every detail of every matter. Completion of a list of obligatory and prohibited things, along with details of a certain number of permitted matters -- that is all any system of law can achieve Naturally the prevalent customs  general practice, and even innovations hardening in time into prevalent usage eye) regulate the relations
in such cases. We shall discuss this further in the chapter on sources of Muslim law.

(14) Besides the laws and customs of the land, treaties between two or more States create obligations. This distinct kind of addition to the fabric of the law is tolerated, for shorter or longer periods, in the interests of the State. The classical Treaty of Hudaiblyah provides us with a precedent of terms even improper in themselves being capable of acceptance with a broader view of the ultimate good of the community.

(15) Further, the distinction between a de jure and a de facto State is necessary, first because sometimes special institutions or happenings (for instance, a powerful rebellion) although not acknowledged as States de jure are yet States de facto. It is possible in special cases that a certain State does not simultaneously possess both the attributes of being de jure as well as de facto. 

Secondly, the aim of this distinction is to point out that we are concerned with foreign Stares as such, and not with foreigners resident in Muslim territory regarding their private affairs, e.g. inheritance, nationality and the like. These belong to Private International Law or The Conflict of Laws as it is also called. In this connection, too, it might be recollected that the Private International Law of Islam is also a part of Fiqh and derives its authority not from any foreign source, but from the sovereign will of the Muslim state itself, which will is subject to the Divine law of the Qur'an. 

Private international law is in itself a vast subject, and could usefully be treated as an independent science, more so because the application of public and private international law depends [upon] different authorities of the State. However, to give a rough idea of what the private international law of Islam is, I add, in this book, no appendix on the subject. I am tempted to do so in order mostly to offer my homage to early Muslim international lawyers who amalgamated the two, and dealt with the details of both in the same works on Siyar.

 (16) In our definition the words "dealings with other . . . States" have a special significance. We intend thereby to convey the idea that Muslim International Law is only that which is observed by a State which acknowledges Muslim law as the law of its land in its dealings with other States. These other States may be Muslim or non-Muslim. We are not concerned with the laws and usages of non-Muslim States, except in so far as the Muslim residents there are concerned, or in so far as those laws and usages have been accepted by the Muslim State to act upon is its international intercourse.

(17) It may be added that, for purposes of illustration, precedents from Orthodox Practice have freely been referred to. These alone are binding. Abnormal and temporary abuse or overlooking of certain rules by a Muslim State can neither legalise the abusive practice nor render the authentic rules null and void. To sum up: If the theologians define Islam as belief in and practice or (i.e. there is no God if not God Himself, and that Muhammad is His messenger), or in a more elaborate form.