Ibn Taymiyyah wrote:

This [type of] piety can lead a person to major [heretical] innovations, for the piety of the Khārijites, Rāfiḍah, Muʿtazilah and their likes is of this type. They abstained from oppression and whatever they considered oppression such as mixing with the oppressers as they claimed, until they abandoned major obligations such as praying congregational and Friday prayers, performance of Hajj and fighting [beneath the authority of the ruler], advising the Muslims and being merciful to them.

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