Reference: Kitaabul-‘Ilm – Page 128, Question No.25
Question: What is the benefit in the students of knowledge learning about the [deviant] sects of the Mu’tazilah, the Jahmiyyah and the Khawaarij, since they do not exist in our time?
Response: Learning about the deviant sects in our time has benefits, [from] which are:
That we know the basis for their [deviated] positions so that we can refute them if we find them, and in reality they do exist; And the questioner saying that they do not exist now [in our time] is based upon his knowledge only. However, that which is known to us and other than us who read about the affairs of the people is that these [deviant] sects are in existence and they are active in propagating their message. And because of this, it is imperative we study their opinions/views so that we know their falseness and know the truth [that we are upon] and refute those [of them] who discourse with us.