Who among the early Muslims first used the term "Aqidah" (creed), and who was the first to introduce it into books of Tawhid (monotheism), and where was it mentioned?

The word "Aqeedah" (creed) has gone through three stages: 1. The linguistic (encyclopedic) stage: Here, it meant firm resolve, collection, intention, the solemnization of contracts, and what a person believes in, whether true or false. 2. The stage of the heartfelt act: Here, "Aqeedah" emerged as a meaning residing in the servant's heart, and in this regard, it is "faith that tolerates no opposite." 3. The stage of maturity and specialization: Here, it became a science and a title for specific issues, meaning "the knowledge of creedal legal rulings derived from definitive proofs and the refutation of doubts."

The word "Aqeedah" itself did not appear in the Qur'an and Sunnah; rather, its linguistic root was present, and the term used in them was "Iman" (faith). This term was used by generations of Muslims to mean the fundamental ideas that a believer must accept and affirm. The first to use the term "Aqeedah" in its current technical sense was Imam Abu Hatim Al-Razi (d. 327 AH) in his book "Asl As-Sunnah wa I'tiqad Ad-Din" (The Foundation of the Sunnah and the Creed of Religion), followed by other imams.