Shaykh Saalih As-Suhaymee said, “In fact, it is incumbent to refute them (the deviants who are firmly rooted in deviance, those who were nurtured upon deviance) with the sayings of Allah and His Messenger (ﷺ) and the narrations of the Salaf and refuting their falsehoods with clear evidences from the Book of Allah and the Sunnah of His Messenger (ﷺ) whilst avoiding obscene speech, cursing and revilement. We have been prohibited from cursing the polytheists if it is feared that it will lead to them cursing Allah and His Messenger (ﷺ).

How much more so with cursing the Muslim who fell into some opposition?

Yes we refute him, the refutation is obligatory, but it should be preceded with sincere advice because the goal is to return the people to that which is correct. The goal is not to destroy [the Muslim]! The goal is to return the people to the straight path.

If the person in question insists and persists in his opposition, and his innovation and his continuance with the people of innovation, then [at that point] it is obligatory to refute him with the legislative means built upon the Book of Allah and the Sunnah of His Messenger (ﷺ)…

Yes, by Allah if he (a person thought to be upon the sunnah) accompanies (ahlu bidah), participates with them in their (innovated) rituals, defends them, and increases their numbers (due to defending them and joining in with their innovated rituals) then by Allah, he is to be refuted…”

Ref: A translation of part of an answer to a question by Shaykh Saalih As-Suhaymee in the Prophet’s Masjid, Saudi Arabia after Fajr on 5th December 2014 (13th Safar Rabi Al-‐Awal, 1436)

Translated by Ismaeel Beaumont

Taken from http://ahlusunnahwaljamaah.com/