Why was the Mu'tazilah given this name?

Question:
Why was the Mu'tazilah given this name?

Answer:
Because they withdrew from the gathering of al-Hasan al-Basri. Their imam was Wasil ibn 'Ata al-Ghassani, who was one of the students of al-Hasan al-Basri (may Allah have mercy on him), the imam of the Tabi'un. A questioner came and asked al-Hasan in his circle, where Wasil was present, saying: "Is the one who commits a major sin a disbeliever or a believer?" Al-Hasan answered that he is not a disbeliever, but rather a believer whose faith is deficient.
This is the answer of the people of the Sunnah: a believer whose faith is deficient. At that point, Wasil ibn 'Ata said: "I do not say that he is a believer, and I do not say that he is a disbeliever. I say that he is in the intermediate position between the two positions." Then he withdrew from al-Hasan's gathering, and his like joined him, and they formed the sect of the Mu'tazilah. Yes.