Does a Muslim become a disbeliever if he fights in a non-Muslim army against Muslims?

During jihād, if a Muslim fights in a non-Muslim army against Muslims due to nationalism or national loyalty, does this take him out of Islam—does he become a disbeliever?

Dear Brother / Sister,

This issue is extremely sensitive and can lead to serious consequences. Therefore, when making a judgment, it is necessary to properly distinguish between belief (ʿaqīdah) and action (ʿamal).

First, let us establish the basic principle:

For a Muslim to knowingly take the side of the enemy against Muslims is a very grave sin and a serious burden. However, this act does not in every case directly entail a ruling of disbelief (kufr). What is decisive is the person’s intention, belief, and how they perceive their action.

1. A situation that constitutes disbelief (kufr)

If a person harbors enmity toward Islam in their heart, considers fighting against Muslims to be justified, rejects or denies the rulings of Islam, then the matter becomes not merely a sin but a problem of belief. Such an attitude leads to disbelief, because here it is not only the action but the belief that is corrupted.

2. A situation that is not disbelief but a very major sin

However, if the person does not deny Islam, does not bear enmity toward Muslims, but makes a wrong choice due to nationalism, fear, coercion, or personal interest, then what they have done is a major sin and a serious deviation, but a direct ruling of disbelief (takfīr) is not given.

The general principle of Ahl al-Sunnah scholars is as follows:

“An act may be disbelief; however, the person who commits it is not declared a disbeliever unless the necessary conditions are fulfilled.”

3. A case of compulsion (ikrāh)

If a person is under threat of death, is forced, and while their heart remains firm in faith is compelled outwardly to act otherwise, then their responsibility is greatly reduced. The Qur’an has granted concession in such cases of compulsion:

“Except for one who is forced while his heart is secure in faith…” (al-Naḥl 16:106)

Thus, a believer who is compelled under severe pressure (ikrāh), while his heart is full of faith, and outwardly expresses or acts contrary to his belief due to that pressure, does not cease to be a believer according to this verse.

4. The issue of nationalism

A particularly important point here is nationalism. If nationalism overrides Muslim identity and disrupts the distinction between right and wrong, it becomes a very dangerous understanding. In Islam, the معيار (criterion) is not race, tribe, or flag, but truth and justice.

For this reason, a Muslim taking a position against Muslims purely due to nationalist feelings reflects a serious weakness and deviation in faith.

In summary:

Fighting in a non-Muslim army against Muslims is a very grave sin and a heavy burden. However, this act is not in every case disbelief.

For it to be disbelief, there must be denial, hostility, or rejection of the religion.

Intention, belief, and circumstances are decisive. In such matters, the most correct approach is not to generalize, not to hastily declare people disbelievers, but also not to underestimate the gravity of the act.

May Allah make us among those who see the truth as truth and follow it, and see falsehood as falsehood and avoid it. Āmīn.

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