Urf

ʿUrf (العرف) is an Arabic Islamic term referring to the custom, or 'knowledge', of a given society. To be recognized in an Islamic society, ʿurf must be compatible with Sharia. When applied, it can lead to the deprecation or inoperability of a certain aspect of fiqh (Islamic jurisprudence).

ʿUrf is a source of Islamic legal rulings where there are not explicit primary texts of the Qur'an and Sunnah specifying the ruling. ʿUrf can also specify something generally established in the primary texts.

Overview
The term 'ʿurf', meaning "to know", refers to the customs and practices of a given society.
 * Terminology

ʿUrf was first recognized by Abū Yūsuf (d. 182/798), an early leader of the Ḥanafī school, though it was considered part of the sunnah, and not as formal source. Later al-Sarak̲h̲sī (d. 483/1090) opposed it, holding that custom cannot prevail over a written text.
 * History

The "maxim" that custom is an authoritative source for Islamic law "appears in the Quran and Hadith". One hadith narrated by Ibn Mas'ud stated 'Whatever the Muslim saw as good is [considered] good by God, and whatever the Muslim saw as evil is evil according to God.'"
 * Scriptural basis

Sharia
Although this was not formally included in Islamic law, the Sharia recognizes customs that prevailed at the time of Muhammad but were not abrogated by the Qur'an or the Sunnah (called "Divine silence" ***sunnah is not "divine silence"). Practices later innovated are also justified, since Islamic tradition says what the people, in general, consider good is also considered as such by Allah (see God in Islam). According to some sources, ʿurf holds as much authority as 'ijma (consensus), and more than qiyas (legal reasoning by analogy). ʿUrf is the Islamic equivalent of "common law".

In the application of ʿurf, custom that is accepted into law should be commonly prevalent in the region, not merely in an isolated locality. If it is in absolute opposition to Islamic texts, custom is disregarded. However, if it is in opposition to qiyas, custom is given preference. Jurists also tend to, with caution, give precedence to custom over doctoral opinions of highly esteemed scholars.

In some countries such as Egypt, marriage, the ʿurfi way, refers to a form of common law marriage that does not involve obtaining official papers issued by the state (زواج عرفي Zawāj ʿUrfi). The validity of that type of marriage is still under debate, and women may have fewer rights than under an officially-registered marriage.