The Noble Scholar Shaykh Muqbil Ibn Haadi, Allah have mercy on him, was asked:
Question: Who is the extremist?
Answer: Extremism/harshness is (that a person) makes prohibited upon the people something that Allah didn’t make prohibited and he obligates upon the people something which Allah didn’t obligate. This is extremism/harshness (in the religion). As for holding on to the religion (as it has been revealed), this is not considered extremism (in the religion).