Before I answer this question, let me make a point about very sad phenomena that occurs in our countries nowadays. There are some people who declare anybody who do not follow their principles, even if those principles are not really part of Islam, an apostate. And there are others who accept anybody who declares himself as a Muslim even if this person does not believe in the fundamentals principles of Islam. Both of these categories of people are wrong.
The definition of Islam is to believe in what the prophet Muhammad had brought to this world. So anybody who believes in this is a Muslim and nobody can declare this person an apostate.
We can then say that there are three categories of Muslim. First category is those people who declare themselves as Muslims but they deny some of the religion. For example, they believe that the prophecy goes even after the death of the prophet or they believe that the Quran that the Muslims have now is not the real one. These category are not Muslim and we have to declare them apostates.
The second category is those who believe in all the principles of Islam but they have some differences regarding some branches of jurisprudence. These are Muslims and we cannot declare them apostate. These are the people who follow Hanafi, Shafii, Hanbali , Maliki and Jafari, and Ibadyya, school.
The third category is those people who do not deny some of the principles of religion but they have differences, not only in ijtihad in some branches of jurisprudence but it goes to some beliefs. These are like the Zaydiya and Aldhahirya.
Sufis have many schools. There are those who want to repair their souls by following the sharia according to the known schools. So they don’t have different believe than what the sharia asks or a method which contradict its rulings. This kind of Muslims go under the second category mentioned before.
However, they are other people who call themselves “Soufia” and they deny some of the religion and they invented ruling unfounded in the sharia. These people go under the first category mentioned before.
Also, they are those who believe in all the principles of sharia but they have some innovations in Islam. So they go under the third category and we can’t not declare them apostates.
Finally, there is the Salafia and they are two categories and we cannot declare them apostates.
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