Muhammad ibn Idris al-Shafi’i (767–820 AD) is the founder of Islamic legal theory (usul al-fiqh) as a formal discipline. His great work, the Risala (‘Letter’), is the first systematic treatment of the sources and methodology of Islamic law. Al-Shafi’i synthesizes the approaches of the Hanafi (rationalist, Iraq-based) and Maliki (hadith-based, Medina-based) schools, insisting that the Sunnah of the Prophet as preserved in authentic hadith must take precedence over local practice or juristic reasoning. His four-source hierarchy — Quran, Sunnah, consensus (ijma), analogical reasoning (qiyas) — becomes the standard framework for all subsequent Islamic jurisprudence. The Shafi’i school is dominant in East Africa, Egypt, Southeast Asia (Indonesia, Malaysia, the largest Muslim populations in the world), and parts of the Middle East.