What caused Imam al-Shafi'i to abandon his old madhhab in Iraq, the Hijaz, Yemen, and the Levant, and to author the new madhhab in Egypt after his interaction with the people of the Maghreb?

It is true that Imam al-Shafi'i (may Allah have mercy on him) dictated books in Egypt that differed from what he had dictated in Iraq. The reason for this was the renewal of knowledge for him, his mastery of principles and rules, and his meeting with scholars from whom he benefited, which led him to change his opinion on many issues. Imam Ahmad advised adherence to the books al-Shafi'i authored in Egypt, saying: "Adhere to the books he authored in Egypt, for he authored those books in Iraq and did not perfect them. Then he returned to Egypt and perfected that." This indicates al-Shafi'i's fairness and his devotion to the truth.