Why did the issue of "madhhabism" (adherence to a specific school of thought) arise, even though the Sunnah of the Messenger of Allah, may Allah bless him and grant him peace, is one? And is it obligatory for a Muslim to follow a specific madhhab, or is it sufficient for him to follow the Book and the Sunnah?

The Prophet Muhammad, peace and blessings be upon him, was sent with Islam, and Muslims were commanded to follow the Quran and Sunnah. The Companions differed in their fatwas due to their varying capacities in memorizing the Sunnah and understanding texts. Later, other reasons emerged for differences among the four imams and others, such as variations in the authenticity of hadith and in the rules for understanding texts (principles of jurisprudence - Usul al-Fiqh).

It is obligatory for a Muslim to follow the Quran and Sunnah, and it is not mandatory for them to adhere to a specific jurisprudential school of thought. The four imams and other imams glorified the texts and commanded adherence to them, forbidding blind imitation of themselves. The madhahib (schools of thought) are systems for understanding the Quran and Sunnah. There is no harm for a Muslim to adhere to a madhhab, provided that they follow the Sunnah if it becomes clear to them, even if it contradicts their madhhab, in accordance with the imams' own recommendations. There is no harm for common people who imitate the imams, as they are commanded to ask people of knowledge. However, they should not be fanatical, condemn others, or issue fatwas themselves.