What is the ruling on marrying someone who follows Mahdawiya and believes that Imam al-Mahdi has already come and gone? And is this belief considered shirk (polytheism) or bid‘ah (innovation)?

The Awaited Mahdi is a man from the nation of Muhammad, peace and blessings be upon him, whose name is Muhammad ibn Abdullah, from the progeny of Al-Hasan ibn Ali, may Allah be pleased with him. He will emerge at the end of time, coinciding with the descent of Jesus, peace be upon him, and will fill the earth with justice and fairness. To claim that he has emerged now is clear misguidance and a refutation of the sound, continuously transmitted (mutawatir) hadiths.

The sects that claim the Mahdi add to this great deviations, among them: equating the Prophet, peace and blessings be upon him, with their alleged Mahdi, declaring anyone who denies their Mahdi a disbeliever, and believing that Islam will be perfected by the Mahdi after the Prophet, peace and blessings be upon him. This is an aspersion against the religion and a refutation of the Quran.

It is not permissible to marry someone who belongs to this misguided sect until he repents and completely disassociates himself from their ideas, because he is either a disbeliever or an innovator with grave innovations. It is not permissible for a Muslim woman to marry a disbeliever or an innovator who corrupts her religion. The scholars have warned against marrying people of innovation, and the four Imams affirmed that religious compatibility is a consideration in marriage. Therefore, the sister must be prevented from marrying this man unless he repents and leaves this sect.