Qiyas

In Islamic jurisprudence, qiyās (Arabic: قياس‎‎) is the process of deductive analogy in which the teachings of the Hadith are compared and contrasted with those of the Qur'an, in order to apply a known injunction (nass) to a new circumstance and create a new injunction. Here the ruling of the Sunnah and the Qur'an may be used as a means to solve or provide a response to a new problem that may arise. This, however, is only the case providing that the set precedent or paradigm and the new problem that has come about will share operative causes (عِلّة, ʿillah). The ʿillah is the specific set of circumstances that trigger a certain law into action. An example of the use of qiyās is the case of the ban on selling or buying of goods after the last call for Friday prayers until the end of the prayer stated in the Quran 62:9. By analogy this prohibition is extended to other transactions and activities such as agricultural work and administration.

Late and modern Sunni jurisprudence regards analogical reason as a fourth source of Islamic law, following the Qur'an, prophetic tradition and binding consensus. While Muslim scholarship in the later period traditionally claimed that analogy had existed in Islamic law since their religion's inception, modern scholarship generally points to Muslim scholar Abu Hanifa as the first to incorporate analogical reason as a source of law. Since its inception, analogical reason has been the subject of extensive study in regard to both its proper place in Islamic law and its proper application.

Among Sunni traditions, there is still a range of attitudes regarding the validity of analogy as a method of jurisprudence. Ahmad bin Hanbal and Dawud al-Zahiri for example, rejected the use of analogical reason outright, arguing that to rely on personal opinion in law-making would mean that each individual would ultimately form their own subjective conclusions.Bernard G. Weiss, one of today's foremost experts on Islamic law and philosophy, explains that while analogical reason was accepted as a fourth source of law by later generations, its validity was not a foregone conclusion among earlier Muslim jurists. Thus, while its status as a fourth source of law was accepted by the majority of later and modern Muslim jurists, this was not the case at the inception of Muslim jurisprudence as a field.

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