From islamqa
It is not possible for a person to be a Muslim and a Communist at the same time, because they are opposites that cannot co-exist in the same individual without one of them prevailing and the other being eliminated. Whoever is a Communist is not a Muslim. Communism involves different kinds of blatant kufr, such as denying the existence of Allaah (may He be glorified and exalted), denying the existence of the unseen worlds, making a mockery of the religion of Allaah and looking down on it, and flouting its laws and morals. How can the Muslim whose religion is Islam follow an ideology which states that religion is the opium of the people? Communists are among the kuffaar in refutation of whom Allaah says (interpretation of the meaning): “Were they created by nothing, or were they themselves the creators? Or did they create the heavens and the earth? Nay, but they have no firm Belief.” [al-Toor 52:35-36] How can the Muslim follow a group whose belief is such? We ask Allaah for guidance.
It is not possible for a person to be a Muslim and a Communist at the same time, because they are opposites that cannot co-exist in the same individual without one of them prevailing and the other being eliminated. Whoever is a Communist is not a Muslim. Communism involves different kinds of blatant kufr, such as denying the existence of Allaah (may He be glorified and exalted), denying the existence of the unseen worlds, making a mockery of the religion of Allaah and looking down on it, and flouting its laws and morals. How can the Muslim whose religion is Islam follow an ideology which states that religion is the opium of the people? Communists are among the kuffaar in refutation of whom Allaah says (interpretation of the meaning): “Were they created by nothing, or were they themselves the creators? Or did they create the heavens and the earth? Nay, but they have no firm Belief.” [al-Toor 52:35-36] How can the Muslim follow a group whose belief is such? We ask Allaah for guidance.
