Ruling on a Muslim woman marrying a Shi’i
Question

                My cousin (daughter of my paternal uncle) is going to marry a Shi’i. What is the Islamic ruling on that? How can I persuade her not to go through with this marriage, knowing that her parents agree to it? Please advise me, may Allaah reward you with good.
Praise be to Allah.
    The Standing Committee was asked the following question: 

    We come from a tribe that lives on the northern borders [of 
    Saudi Arabia], and we mix with tribes from Iraq who are idolatrous Shi’ah; 
    they worship domes and call them al-Hasan and al-Husayn and ‘Ali. When one 
    of them stands up he says. “O ‘Ali, O Husayn.” Some people from our tribe 
    have intermarried with them and mix with them in all circumstances. We have 
    tried to teach them but they do not listen. I do not have enough knowledge 
    to teach them but I hate what they do, and I do not mix with them. I have 
    heard that we cannot eat meat slaughtered by them, but these people eat 
    their meat and do not care. We are asking you what are our obligations in 
    this case? 

    Answer: 
and blessings and peace be upon His 
    Messenger and his family and  companions. 
    
    If the situation is as you describe – that they call upon 
    ‘Ali, al-Hasan and al-Husayn, and so on – then they are mushrikeen who are 
    guilty of major shirk, which puts them beyond the pale of Islam. It is not 
    permissible for Muslim women to marry them, and it is not permissible for us 
    to marry their women, or to eat meat slaughtered by them. 

    Allaah says (interpretation of the meaning): 

    “And do not marry Al-Mushrikaat (idolatresses) till they 
    believe (worship Allaah Alone). And indeed a slave woman who believes is 
    better than a (free) Mushrikah (idolatress), even though she pleases you. 
    And give not (your daughters) in marriage to Al-Mushrikoon till they believe 
    (in Allaah Alone) and verily, a believing slave is better than a (free) 
    Mushrik (idolater), even though he pleases you. Those (Al-Mushrikoon) invite 
    you to the Fire, but Allaah invites (you) to Paradise and forgiveness by His 
    Leave, and makes His Ayaat (proofs, evidences, verses, lessons, signs, 
    revelations, etc.) clear to mankind that they may remember”

    [al-Baqarah 2:221]
And Allaah is the Source of 
    strength. May Allaah send blessings and peace upon our Prophet Muhammad and 
    his family and companions. 

    From Fataawa al-Lajnah al-Daa’imah, 2/264 
You have to advise your 
    uncle and cousin, and tell them about the fatwas of the scholars concerning 
    this issue. If your uncle insists on marrying his daughter to a Shi’i, then 
    refer the matter to the sharee’ah court to prevent this evil action. 

    And Allaah knows best. 

    See also question no. 
    4569.