By a brother:

The science of tazkiyah (spiritual purification) has been known by derivatives of the word taṣawwuf from as early as the second century, just as the science of Islamic law has been known as fiqh for many centuries. There can be no considerable difference of opinion on the permissibility of using the term taṣawwuf to refer to the ❝science of spiritual purification❞ as people are permitted to coin any term they prefer for any meaning.

The usual response to the above by some is, ❝Did the Prophet ﷺ or the companions use the word taṣawwuf to refer to tazkiyah?❞ The answer again is: It doesn’t really matter. There is no prohibition in using a term that the Messenger ﷺ or his companions did not use. In fact, we do this in many sciences including ‘aqīdah (theology) itself; for the word ‘aqīdah was not used by the Messenger…