The Holy Quran and the Sunnah (tradition) are the primary sources of Shariah (Islamic law) whereas Ijmaa (consensus of opinion) and Qiyaas (analogical deduction) are the secondary sources of Shariah because they depend on the two primary sources and have no authority if repugnant to the Quran and the Sunnah.
Ijtihaad (free explanation within the originally established rules of legal inquiry and moral norms) is the name of a process that literally means to strive or struggle and in legal terminology it is a juristic exercise in which a Muslim jurist utilises his intellectual and legal expertise for finding solution to those matters that are not directly covered by the two primary sources of Shariah, namely the Quran and the Sunnah. Ijtihaad, in fact, it is the dynamic and creative interpretation of Islamic law. After carrying out Ijtihaad when the jurists agree on some way-out, it becomes Ijmaa and if it is the individual opinion of a jurist then it is Qiyaas. So basically Ijtihaad is an exercise, the net result of which may be either in the form of Ijmaa or Qiyaas/analogical deduction. On account of Ijtihaad, Islamic laws are free from stagnation and retain the capacity to develop/prosper with each passing day. Ijtihaad enables the Muslim jurists to solve any legal issue that may arise at any moment of time in consonance with the Quran and the Sunnah.
In addition to these four sources vis-Ã -vis the Holy Quran, the Sunnah, Ijmaa and Qiyaas, there is also some other additional sources of Shariah, namely Istihsaan, Masalih al-Mursala wal Istislah, Istadlaal and customs/traditions. Although the later four sources are not as prominent as the former four ones, yet these additional sources have also played a significant role in the development of Islamic Jurisprudence.
Here is the brief description:
ISTIHSAAN:
Istihsaan literally means preferring or considering a thing to be good. Muslim jurists like Sir Abdur Rahim have translated it as ‘juristic preference or equity’. It is a doctrine which enables a jurist to refuse a doctrine of analogy either because it is opposed to a Quranic/Hadith text or consensus of opinion or is such that his better judgment does not approve of it. For example, if it happens that a law derived from analogy is in contravention of the text of the Holy Quran, the Hadith or Ijmaa or obstructs public welfare or juristic principles then, according to the Hanafi law, jurists are empowered to replace it with a rule that better serves public welfare and principles of justice.
On the basis of Istihsaan, the Hanafi jurists give up rules of analogy in favour of rules sanctioned by the custom being more acceptable to people.
Istihsaan is used only by the Hanafis as a source of law, and they term it as specie of analogical deduction. They term it hidden analogy although it is having wider scope, then analogical deduction. This doctrine has largely helped to develop the Hanafi jurisprudence, the founder of which deserves the credit of having been the first to recognize that a strict adherence to analogy would deprive the Law of Elasticity and Adaptability, which are important features of the Islamic legal system. The Shaafis and Malikis do not accept Istihsaan as a source of Islamic jurisprudence and Shaafi is reported to have said ‘whoever resorts to Istihsaan makes laws. On the basis of Istihsaan, the Hanafi jurists give up rules of analogy in favour of rules sanctioned by the custom being more acceptable to people.
PUBLIC GOOD:
In relation to Istihsaan, Imam Malik has allowed a deduction of law to be based on the general consideration of public good known as Masalih al-Mursala wal Istislah. But this principle is vague and owing to lack of clarity, it has not played an effective role in development of the Malaki School of Thought because it cannot be easily distinguished from analogical deduction which also advances public good. For example, some Malaki jurists have invoked this doctrine to justify use of force to a person accused of theft to make him confess. However it is better that a guilty person should escape than that an innocent person should be subjected to ill-treatment. Due to lack of clarity this doctrine failed to attain prominence and importance among Muslim jurists.
ISTADLAAL:
Istadlaal means inferring one thing from another. The Hanafi jurists use it in the context of interpretation. Interpretation is quite different from analogical deduction. In interpretation, law is deduced from the language of the text whereas in analogical deduction law is not deduced from the text but is derived from the reason of the text. The Malakis and Shaafis disagreeing with Hanafis do not consider Istadlaal as a mere interpretation or analogy but they term it as a comprehensive method of logical reasoning which enables a jurist to derive law.
The connection between two propositions with an effective cause is Qiyaas or analogy, whereas without an effective cause comes within the scope of Istadlaal. For example, some jurists have opined that if a regular Wadu (ablution) is valid without specific intention, a substitute Tayamum (ablution) is also valid without specific intention. This is not the accepted view of Hanafis. The presumption that the state of things that are not proved, have ceased or still continue, falls within the ambit of Istadlaal.
The authority of revealed laws prior to Islam is also based on Istadlaal as the Islamic doctrine clarifies that all those teachings of previous prophets that have not been abrogated by Islam are worthy of obedience. This is in respect of those prophets whose mention is found in the Holy Quran and the Hadith as we find names and references of 25 Prophets in the holy book; and six Surahs (chapters) of the Holy Quran are on the names of Prophets.
The authority of revealed laws prior to Islam is also based on Istadlaal as the Islamic doctrine clarifies that all those teachings of previous prophets that have not been abrogated by Islam are worthy of obedience.
CUSTOMS AND USAGE:
The customs and traditions are also recognised by Islam as a source of law. Those customs and traditions of Arabia which prevailed during the life of the Holy Prophet (peace be upon him) and were not repealed or altered by the Quranic verses or the Hadith are valid and binding on Muslims; because silence of the Holy Quran and the Hadith about such customs is treated as a tacit approval. Such customs and traditions slightly resemble Sunnat-ul-Taqeer, which consists of those actions of the Companions (may Allah be pleased with them) as were carried out in front of the Holy Prophet (peace be upon him) and he did not prohibit their occurrence. Certain family laws of Muslims relating to paternity, marriage, divorce, guardianship, dower, period of probation, maintenance etc are having some reliance upon customs and traditions of Arabia. The authority of those customs and traditions which originated in the Muslim society after the sad demise of Prophet Muhammad (peace be upon him) is based on his sayings in which he said, ‘Whatever the people hold to be good is good before Almighty Allah.’
Customs as a source of law resemble analogical deduction as both are having no authority if repugnant to the Holy Quran, Hadith or Ijmaa by the learned jurists. However in respect of the legal authority, it is superior to analogical deduction if it is not in contravention of the Holy Quran, the Hadith and valid Ijmaa. The customary law is inferior to Ijmaa as it is based on the practice of general public, whereas Ijmaa is the considered opinion of Muslim jurists who are well-versed in Fiqh as the Holy Quran declares that literate and illiterate people are not equal. At another place, Allah Almighty says that literate people are like those who are having vision and illiterate people are like those who are blind.