He was active in juridical matters and his teaching eventually led to the school of fiqh named after him. Hence he is often called Imam al-Shafi'i. The Greatest Imam among the Four Imams of Fiqh, in terms of vast knowledge and authority. Scholars gave him the honorific title "Father of Usul Al-Fiqh" (The Patriarch of the Foundation of Islamic Jurisprudence). His full name was Abu Abdullah Muhammad ibn Idrīs al-Shafi'i.

He authored more than 100 books. Al-Risala — The best known book by al-Shafi'i in which he examined usul al-fiqh (sources of jurisprudence): the Qur’an, the Sunnah, qiyas (analogy), and ijma' (scholarly consensus). There is a good modern translation.

He also divided innovation into good and bad, based on the hadith of Umar about tarawih.