Who was the first to compile works on aqidah (Islamic creed/theology)?

Scholars have not precisely identified the first to author works on aqidah (creed), but documentation began during the lifetime of the Tabiin (successors) at the hands of Imam Al-Zuhri, then became widespread in the second Hijri century.

Imam Malik's categorization of hadiths in "Al-Muwatta'" was an initial nucleus for the independent classification of chapters on Tawhid (monotheism). The innovations (bidah) and doctrinal differences that emerged at the end of the Sahabah's era ignited the drive for documentation.

The first known compiler in aqidah is the book "Al-Fiqh Al-Akbar" by Imam Abu Hanifah (d. 150 AH), in which he defined the beliefs of Ahl Al-Sunnah and refuted opposing sects. He is considered the founder of the science of Tawhid, in the sense of being the first among Ahl Al-Sunnah to author a specific work in this field.

The book "Al-Fiqh Al-Akbar" has also been attributed to Imam Al-Shafi'i, but this attribution is not authentically documented.

Following this, numerous works in the science of Tawhid appeared under various names, such as "Al-Iman" by Abu Ubayd Al-Qasim ibn Sallam, "Al-Sunnah" by Ibn Abi Shaybah and Imam Ahmad, and "Al-Tawhid" by Ibn Khuzaymah.

The terms "Usul Al-Din" (fundamentals of religion) and "Al-Aqidah" (creed) emerged in subsequent centuries, and the movement of authorship became stable.

This refutes those who claim that Abu Al-Hasan Al-Ash'ari and Abu Mansur Al-Maturidi were the founders of the science of Tawhid, as many works preceded them, following the methodology of Ahl Al-Sunnah wa Al-Jamaah.