Is it permissible for Muslims to dispute among themselves due to a difference of opinion, under the pretext that the disagreement is over religious beliefs and fundamentals? And what are these fundamentals and beliefs over which disagreement is impermissible and for which disputing is permissible if disagreement occurs?

It is not correct to deal with all types of disagreements in the same way. A distinction must be made between legitimate and acceptable disagreements, and illegitimate and reprehensible ones. The former does not contradict a text or a consensus, unlike the latter which relies on whims or mere opinion.

In the case of illegitimate disagreements, the false statement must be denounced and its weakness clarified. As for the one who made the statement, their situation should be considered:

- If they are among the people of knowledge and integrity and made a mistake in the issue, their status is preserved and their statement is rejected. - If they are among the people of whims or those who dare to issue fatwas without knowledge, they are dealt with through sincere advice, enjoining good and forbidding evil. If they do not accept, they are dealt with in a way that quells their mischief, such as shunning and boycotting, and their matter is referred to the ruler for punishment.

For further details, refer to the book "Al-Khilaf: Anwa'uh, wa Dawabituh, wa Kayfiyat al-Ta'amul Ma'ah" (Disagreement: Its Types, Controls, and How to Deal with It) by Hasan al-Osaimi.