In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear questioner, thanks for the great confidence you place in us, and we implore Allah Almighty to help us serve His cause and render our work for His Sake.
The Qur’an, which is the main source of Islamic legislation, contains the most important rules of international law concerning peace, war and treaties. In addition, one of the basic features of Islamic Shari`ah is that it is flexible and suitable for all times and places.
In an attempt to furnish you with the answer to your question, we would like to cite for you the following fatwa issued by the late Sheikh Jad Al-Haqq `Ali Jad Al-Haqq, former Grand Sheikh of Al-Azhar, in which he states the following:
There is no doubt that the main sources of the Shari`ah are the Qur'an and the Sunnah in addition to the consensus of Muslim scholars (’ijma`) and the personal judgment of Muslim scholars in conformity with the prescriptions of the Qur’an and the Sunnah (ijtihad). There are different types of religious texts: General definitive texts such as Allah's saying: (O ye who believe! Fulfill your undertakings) (Al-Ma'idah 5: 1), (…and (He Almighty) hath not laid upon you in religion any hardship) (Al-Hajj 21: 78), (Squander not your wealth among yourselves in vanity) (An-Nisaa' 4: 29), special definitive texts such as the verses stating the regulations of inheritance and those prohibiting riba (usury), adultery, drinking alcohol drinks and gambling. There are also other types of sources such as the consensus of Muslim scholars on such matters as the annulment of the marriage of a Muslim woman to a non-Muslim and the responsibility of the husband for his wife's maintenance. Moreover, the prescriptions of the Sunnah are also considered religious texts such as the saying "prohibition by fosterage is tantamount to prohibition by lineage".
In this framework, rulings governing life activities, administrative, economic, commercial and criminal codification are all derived from the previous sources as long as they abide by the general rules of the Islamic legislation. However, there is not a chance now to cite the verses of the Qur'an that state or refer to legal rules in various branches of law.
The Glorious Qur’an contains the most important rules of international law concerning peace, war and treaties. For instance, it contains the rule of reciprocity in addition to the rules governing the POWs and the necessity of declaring the annulment of a treaty even if it is unjustified. In this respect, a Muslim jurist says, "Honoring commitments without deception is better than reciprocal deception".
In the Glorious Qur'an, there is a call for peace and for reconciling disputing parties as well as deterring aggressors. Moreover, there is a call for equality and resorting to reason, evidence and amicable debate in order to arrive at what is right. The Qur'an also states that men and women are equal concerning competence and preserves a woman’s right to freedom of expression in addition to preserving her individual liberty so that it does not dissolve to her husband's custody as it is the case in most Western laws which we unfortunately try to imitate. The Qur'an also contains general rules of civil transactions, the codes of civil and criminal evidence, the rules governing marriage and divorce. It also settles the matters related to the rights of the spouses both during marital life and in case of divorce, in addition to stating the rights of offspring, parents and relatives. The Glorious Qur'an also gives definitive penalties for crimes threatening the state security, while there are other crimes in which those in charge have discretion to set down penalties, these are actually open to ijtihad (personal judgment) and are liable to amendment and alteration according to the advancement of time. That is what is meant by the famous saying that Shari`ah is suitable for all times and places. That is because its flexibility makes it vivid.
Moreover, there is no objection whatsoever to resorting to custom and traditions provided that they do not contradict a definitive text in the Qur'an or Sunnah or a previous consensus of Muslim scholars concerning a certain matter. For instance, when the Islamic state expanded, `Umar ibn Al-Khattab made use of the experience of the Persian and Roman as regards secretarial works in addition to their system of levying taxes. He even employed them to carry out these tasks and to train Muslims to do them. Therefore, we can copy things that do not contradict the principles of Islam.
In fact, the authoritative books on fiqh or Islamic jurisprudence, with the opinion of all the renowned jurists, deal with the problems of our society in a way that goes in line with the spirit of our age without any harshness or violation of the general and special Islamic definitive rules. These rules must be the main reference for all codifiers and reformers instead of importing foreign rules alien to our traditions. If we really do so, we will find that our Islamic legislation is compatible with the contemporary civilization and guides the society safely towards peace and security and preserves our religion and traditions so that Allah may be pleased with us, for He made us the best nation on earth when He says, (Ye are the best community that hath been raised up for mankind; ye enjoin right conduct and forbid indecency, and ye believe in Allah.) (Aal- `Imran 3: 110)
Allah Almighty knows best.