The importance of studying Muslim law can be estimated from the fact that:
It applies to approximately 20 crore Muslims in India, 15 crores in Pakistan and 15 crore in Bangladesh. The overall world, Muslims are in some twenty countries of Asia, Africa and Europe, and they follow Muslim law in the form of either civil law or both civil and criminal law. The number of Muslims around the world is rapidly increasing, growing from 1.6 Billion in 2010 to 2.8 Billion in 2050 approximately.

Islamic law came to Asia, Africa and Europe through the expansion of the Ottoman Empire and in India, it came with the Mughal and Delhi Sultanate. In India, Muslim Law means "that portion of Islamic Civil law which is applied to Muslims as a personal law" (Fyzee). It contains the ruling of the Quran, the tradition of the Prophet Muhammad (pbuh) [sunnah], the Consensus of opinions (ijma) and the analogical deduction of these three (Qiyas).

In this article, I will discuss the Source of Muslim Law in two sources;

1. Primary Sources:
   1. The Quran.
   2. The Sunnat and Ahadis.
   3. The Ijma.
   4. The Qiyas.
2. Secondary Sources:
   1. The Urf or Custom.
   2. Judicial decisions.
   3. Legislation.
   4. Justice, equity and good conscience.

Primary Sources:

1. The Quran: The word Quran has been derived from the Arabic word Quarra, which means to read. It contains the word of God, which is transmitted to Prophet Muhammad (pbuh) through the angel Gabriel. There are 114 Chapters in the Quran, which comprise approximately 6666 verses, of which 200 are concerned with legal principles, and 80 are concerned with marriage, dower, divorce and inheritance. The Verses of the Quran are called Ayat, and the chapters are called Sura. Chapters in the Quran are not arranged in chronological order but as commanded by the Prophet. The Chapters were arranged under the personal direction of the Prophet, who used to ask the scribe present to insert the revealed verses in a particular chapter. The Quran was revealed in its complete form in 23 years (609 to 632 AD). The portion that is revealed in Madina is concerned with legal principles, and the portion that is revealed in Mecca deals with the philosophy of life and the Islamic religion. It was collected by the First Khalifa Abu Bakar (r.a), arrangement of whole Sacred book into textual form by the Third Khalifa Usman (r.a) under the supervision of the following experts: Zaid, the son of Thabit; Abdullah, the son of Zubair; Said, the son of As; and Abdur Rahman, the son of Harith. Usman (r.a) made several copies and sent them to different centres of Islam, and these became texts for all subsequent copies of the sacred book. The Islamic religion and society owe their origin to the Quran. It is the paramount source of Muslim Law because it contains the very words of God and its foundation upon which the exact structure of Islam rests. The Quran regulates the individual, social, secular, and spiritual life of Muslims.
    
2. The Sunnat and Ahadis: God makes two types of revelation to the Prophet through Angel Gabriel: One is Zahir, and the other is Batin. Zahir revelation is the direction of God to Prophet Muhammad (pbuh) in the very words of God; the Quran is the Zahir revelation. Batin revelation consisted of the opinions of the Prophet, which was delivered from time to time on the raised questions; Ahadis is considered the batin revelation from God to the Prophet Muhammad (pbuh). Whatever Prophet pronounced in his verdict related to any particular matter permitted any act and prohibited any of them; keeping silent on any act in his lifetime became the Primary Source of Muslim Law in the form of Ahadis. In simple meaning, Whatever the Prophet said, did or tacitly allowed in his lifetime is called Ahadis or Tradition; it was not written down during the lifetime of the Prophet but preserved as tradition and handed down from generation to generation by authorised persons. That's why before accepting Hadis, a mandatory inquiry was done to check its authenticity. When a Hadis is confirmed by one person, that Hadis is considered weak Hadis or Khabar-al-Wahid, which is proved by several declarations, it is regarded as strong Hadis. The Quran listed the importance of Hadis as a source of Muslim law in several verses. The Quran says: "Whatever the prophet gives, accept it, and whatever he forbids, you abstain from it." It also says: "He does not speak out of his desire. It is not but the revelation to him." "Obey God and obey the messenger." Once, the prophet said, "So long as you hold fast to two things which I have left among you will go astray, God's Book, and His messenger's Sunnah."
    
3. The Ijma: According to Sir Abdul Rahim, Ijma is an agreement of the jurists among the followers of Prophet Muhammad (pbuh) at a particular period on a particular question of law. Wilson considered the meaning proposition shown to have been accepted as indisputable under the first four rightly directed Caliphs or in the time of the companions and of the generation immediately succeeding them. Subsequent Ijma of the same age may reverse Ijma of one age. Similarly, Ijma of one age may be suspended by ijma of subsequent age. But the Prophet's Companions Ijma cannot be reversed or suspended by the later Muslim jurist ijma. The Quran and Hadis, in various places, talk about the importance of Ijma as a source of Muslim Law. "O ye who believe; obey God and obey the Prophet and those of you who are in authority, and if ye have a dispute concerning any matter refer it to God and the Prophet." Once Prophet Muhammad (pbuh) says, there can be no consensus on error or misguided behaviour among my people. According to Hanafi Law, "Law must change with the changing of times," and Maliki School's view that "new facts require new decisions. The aim of the law must be to fulfil the needs of the society in the changing times." After the death of Prophet Muhammad (pbuh), the principle of ijma was the only way to solve the numerous problems because the Quran and Hadis do not have explicit answers to every situation.
    
4. The Qiyas: It is a reasoning by analogy of the above three sources: the Quran, the Sunnah and the Ijma; in Qiyas, rules are deducted by the exercise of reason. It can be defined as a process of deduction in which the law of the text is applied to cases. It doesn't create new laws but merely applies the old established principle to new circumstances. All Four Schools of Sunni Law consider it a valid source of Muslim Law, but Shia don't consider it a valid source of Muslim law. But the Quran and Hadis in various places talk about its importance: "Learn a lesson, O ye who have vision to see."

The Holy Quran often says:
"Ye men of wisdom take a lesson". The Prophet said, "Give your ruling by the provision of this Book ( the Quran) and the Sunnah; if you do not find such provisions, have resources for your opinion and interpretation." When Mu'adh (r.a) was being sent to Yemen, the Prophet asked him on what basis you will make a decision. He replied that I would judge them first according to the Book ( the Quran), then Sunnah, and if I didn't get an answer from the Quran and Sunnah, then I would follow my reason. Qiyas was upheld by the Prophet both by precept and practice. Even in the caliphate period, it was not questioned. According to Imam Abu Hanifa, Sunni law has evolved due to the recognition of this institution.

Secondary Sources

1. The Urf or Custom: It was never formally recognised as a source of Muslim Law but referred to as supplementing it. Those customs and usage of the people of Arabia, which were not expressly repealed during the lifetime of the Prophet, were accepted as a valid practice or rule in Islamic Law. In Hidaya, Custom has considered haa the same rank as Ijma. Customs are territorial in their very essence, so one country's customs cannot affect the general law of other countries. In India in 1937, the Shariat Act was passed to abolish all the customs which is contrary to the Shariat and to restore the law of Islam in the true sense.
    
2. Judicial Decision: Judicial decision declares the law as it is, and the decision of the court supplements and modifies the law; Muslim Law is no exception to this rule. Like under the Muslim Law, no interest is allowed on a loan, But in Hammeera Bibi v. Zubaida Bibi, the Privy Council allowed interest on the amount of unpaid dower.
    
3. Legislation: In India, Muslims are governed by the various legislation passed by the Parliament or the State Legislature. Like the Freedom of Religion Act of 1850, the Guardians and Wards Act of 1890, the Mussalman Wakf Validating Act of 1913, the Mussalman Wakf Validating Act of 1930, the Wakf Act of 1954, the Child Marriage Restraint Act of 1929, the Shariat Act, 1937, the Dissolution of Muslim Marriage Act, 1939, Muslim Women (Protection of Rights on Divorce) Act, 1986, the Wakf Act, 1995, the Waqf (Amendment) Act, 2013, the Prohibition of Child Marriage Act, 2006 and the Muslim Women (Protection of Rights on Marriage) Act, 2019.
    
4. Justice, equity and good conscience: Abu Hanifa, the founder of the Hanafi sect of Sunnis, expounded the principle that the rule of law based on analogy could be set aside at the option of the Judge on a liberal construction or juristic preference to meet the requirements of a particular case.

Reference:

• The Holy Quran
• Aqil Ahmad, Mohammedan Law (23rd edn, CLA 2011)
• Syed Khalid Rashid, Muslim Law (5th edn, EBC 2017)