O’ Noble Shaykh, there comes in a ḥadīth from the Prophet ﷺ:
A people will come in the latter days of time that will pierce through (and exit) Islam like how an arrow pierces through its target”. We kindly request from you a clarification of their characteristics and the manner in which they pierce through Islam (marooq).

Shaykh Muḥammad ibn Ṣāliḥ al-ʿUthaymīn:

These people are the khawārij whom the Prophet ﷺ described as being people of (seemingly) religious obedience and worship; and that one of the companions would belittle his prayer in comparison to their prayer and his recitation of Qurʾān in comparison to their recitation of Qurʾān. However, these actions of religiousness do not go beyond their throat, meaning: it does not descend to (is not digested by) the heart – Allāh’s refuge is sought – thus they pierce through Islam like the piercing of an arrow shot through its target. When an arrow hits a target (or prey), it pierces it at high speed and exits from the other side. The khawārij are like this. They pierce Islam, passing through it quickly like the speed of an arrow and then exit from it – we ask Allāh for wellbeing.