Qiyas (Arabic: قياس, qiyās [qiˈjaːs], lit. 'analogy') is the process of deductive analogy in which the teachings of the hadith are compared and contrasted with those of the Quran in Islamic jurisprudence, 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 Quran 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. Among Sunni Muslims, Qiyas has been accepted as a secondary source of Sharia law along with Ijmāʿ, after the primary sources of the Quran, and the Sunnah.

Late and modern Sunni jurisprudence regards analogical reason as a secondary source of Islamic law along with binding consensus, following the Quran, and prophetic tradition. While Muslim scholarship in the later period traditionally claimed that analogy had existed in Islamic jurisprudence since their religion's inception, modern scholarship generally points to Muslim scholar Abu Hanifa as the first to incorporate analogical reason as a secondary 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. Imam Bukhari, Ahmad ibn 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.

Opposition to qiyas came from a number of angles. Professor Walîd b. Ibrâhîm al-`Ujajî of Imam Muhammad ibn Saud Islamic University explains the opposition to qiyas as coming from multiple angles:

Scott Lucas, when mentioning Ahmad Dallal’s position on Salafism, states that Dallal:

Imam Bukhari maintained a negative position towards qiyas, as he held views aligned with the Zahiris of his time. Scott Lucas states that Bukhari’s rejection of qiyas was placed within the context of what Bukhari perceived as invalid techniques of ijtihad, which included religious innovation (bid’a), ra’y, and tamthil.^{[citation needed]}

Lucas also points out common mistakes other scholars make when analyzing Bukhari’s position on qiyas. The biggest source of confusion for scholars is the fact that, while rejecting qiyas, Bukhari accepts the idea of tashbih (comparison), which seems similar to analogy. However, this is not the case, as tashbih is a comparison used in explanation (such as a metaphor), whereas qiyas applies a specific legal ruling to another case.

Bukhari is also known for his criticism of those who say that the Prophet used qiyas, and he devoted a section of his Sahih to the topic. Bukhari states: