Abū Isḥāq Ibrāhīm ibn ʿAlī al-Shīrāzī (Arabic: أبو إسحاق الشيرازي) was a prominent Persian[6] jurisconsult, legal theoretician, theologian, debater and muhaqqiq (researcher).
[7] He was one of the leading scholars of Shafiʿi jurisprudence in the eleventh century and arguably the most prolific writer of Islamic legal literature.
[8][9] He became the second teacher after succeeding Ibn al-Sabbagh at the Nizamiyya school in Baghdad, which was built in his honour by the vizier (minister) of the Seljuk Empire Nizam al-Mulk.
In 415 AH (1024–1025 AD), he entered Baghdad to study under Abu al-Tayyib al-Tabari the foremost Shafi'i jurist of his time.
He remained most of his lifetime in Baghdad and showcased his profound skills and intelligence in sacred law replacing himself as the mufti of the Muslim Ummah (Islamic community) in his time.
Energised by their shaykhs, the Hanbalis assembled in the al-Qasr mosque and invited Abu Ishaq and his followers to fight alongside them against prostitution, interest charges, and wine-drinking.
[20] On his death, his pupils sat in solemn mourning in the Nizāmiya college, and after that ceremony, Muwyyad al-Mulk, son of Nizam al-Mulk, appointed Abu Sa'd al-Mutwalli to the vacant place, but when Nizām al-Mulk heard of it, he wrote to disapprove of that nomination, adding that the college should be shut up during a year, on account of Abu Ishaq's death; he then blamed the person who had undertaken to fill his place, and ordered the sheikh Abu Nasr ibn al-Sabbagh to profess in his stead.
[1] Abu Ishaq was a stuanch Ash'arite who defended and propagated the doctrine in his book called Al-Ishara ila Madhhab Ahl al-Haqq.