in classical Islamic theory, the four major sources from which law is derived: the Qur'an; the sunna, or sunnah (practice of the Prophet as transmitted through his sayings); ijma' (consensus of scholars); and qiyas (analogical deductions from these three). The usul, systematized under ash-Shafi'i (767820), were the result of an Islamization of law that began about the 2nd century of the Muslim era (8th century AD). Law existed apart from religion under the first four caliphs and the Umayyad dynasty and was generally administered through existing pre-Islamic institutions of foreign (Roman, Byzantine, Jewish, Persian) character. Pious Muslim scholars, who were later grouped into the ancient legal schools of Iraq, Hejaz, and Syria, began to reinterpret the law in an Islamic light. Ash-Shafi'i completed this Islamization process by establishing a norm for interpretation, the usul, but the functions of the individual principles were fixed in legal theory by later scholars.
USUL AL-FIQH
Meaning of USUL AL-FIQH in English
Britannica English vocabulary. Английский словарь Британика. 2012