Extremism originally means to go beyond the proper limits, or to exceed them, or to overstep all bounds.
Accordingly, extremism in the religion is defined as the act of exceeding the proper bounds or limits in the religion and showing harshness in its practices.
It is this meaning that the holy Qur'an pointed to when Allah the Almighty says: "O people of the scripture (Christians)! Do not exceed the limits in your religion, nor say of Allah aught but the truth" (Qur'an: 4, Verse:171). As the prophet of mercy Muhammad (may peace and blessings of Allah be upon him) also emphasized the same meaning in his tradition which states: "Beware of extremism in the religion" (An- Nasai and Ibn Majah).
The prominent scholar Sheikh Sulayman ibn Abdullah (may Allah have mercy on him) tried to shed more light on this definition by specifying the criterion of extremism as he says: "Its criterion is to go beyond what Allah the Almighty Has ordered. It is the transgression prohibited by Allah in His saying: "(Saying) eat of the Tayyibat (good lawful things) wherewith We have provided you, and commit no transgression or oppression therein, lest My Anger should justly descend on you. And he on whom My Anger descends, he is indeed perished" (Qur'an: 20, Verse: 81).
In spite of the above, "the truth is the intermediate between negligence and excessiveness, and whoever stay away from both has been truly guided".
Types of Extremism:
Extremism are of two types:
First: Extremism related to the Creed, which means overstepping the bounds of the correct and proper beliefs in a particular religion.
Among the examples of extremism related to creed are:
1- Christian extremism about I'sa bin Maryam (Jesus) by giving him divine attributes.
2- Shites extremism about Ali bin Abi Ta'lib (may Allah be pleased with him), whereby part of them claimed him to be God, while others believe that he is infallible.
3- Extremism of some Sufis about the holy prophet (may Allah's peace and blessings be upon him) when they claimed he was created from the light and that the whole universe was created from his light. They also belief that the last prophet has the ability to effect the universe and to influence anything in the heaven and the earth as he wishes.
4- Extremism of ordinary Muslims about some religious scholars, righteous leaders and Shaykhs by appealing to them and asking them for help on things which no one can provide except Allah the Almighty.
Second: Extremism related to deeds, it is any kind of extremist act that falls within the range of the five legal rulings, namely: obligatory, recommended, prohibited, disapproved, permissible. Therefore, whoever makes a recommended issue obligatory, or a disapproved issue prohibited, or a permitted issue disapproved has held to extremism in his deeds.
Similarly, If a person makes the night prayer (tahjud) obligatory for himself, he has become an extremist based on this action, because he placed a recommended matter in place of obligatory one and he has exceeded the bounds of Sunnah in this aspect.
The same thing applies to whoever prohibits what Allah Has permitted such as marriage, having desire that he is worshiping Allah with such act.
Shaykhul Islam Ibn Taymiyyah (may Allah have mercy on him) says: "Extremism manifests, at times, by making what is neither obligatory nor recommended in worship obligatory or recommended. And at times by placing what is neither prohibited nor disapproved (out of good things permitted by Allah) in the position of prohibited and disapproved things".
It is necessary to clarify that extremism related to the creed is more dangerous and more harmful than extremism related to the deeds. Extremism related to the creed is the one that causes a religion to split and consequently the emergence of different sects that go beyond the straight path.