Marrying A Shia

Mufti Abdur Rahim Laajpuri Rahmatullahi Alaih has written that there are those Shias whose beliefs are certainly corrupt but not to the extent that it reaches Kufr (such as for example if they only believe that Hadhrat Ali Radhiallahu Anhu was superior than Hadhrat Abu-Bakr Radhiallahu Anhu. This belief would render the person a Faasiq but not a Kaafir).
[Ref:- Fataawa Rahimiyyah pg.189 vol.8]. 

However, there are also such Shias whose beliefs do take them into Kufr. It is not permissible to participate in the Janaazah of such Shias (whose kufr is established), in fact they should be dumped into a hole (when they pass away).
[Ref:- Fataawa Daarul Uloom Deoband pg.375 vol.5].   

With regard to those Shias whose beliefs render them Kaafir and what type of beliefs those are, Allamah Shaami (Rahimahullah) writes in Raddul Muhtaar:

“If a Raafdhi/Shia believes that Allah Ta’aala makes himself manifest (Naoozhu billah!) in the form of Hadhrat Ali (Radhiallahu Anhu), or that  Hadhrat Jibreel (alaihis salaam) erred in taking the Wahi to Rasulullah sallallahu alaihi wasallam (meaning that he should have taken it to Hadhrat Ali Radhiallahu Anhu), or he denies the Sahabiyyat status of Hadhrat Abu Bakr Radhiallahu Aanhu or he accuses Ummul Mu’mineen Hadhrat Ayesha Siddiqah (Radhiallahu Aanha) of adultery (Naoozhu billah!) then such a person is a Kaafir
[Raddul Muhtaar, Vol. 4, Pg. 237 H.M. Saeed Edition]. 

Apart from the above, there are several other corrupt beliefs of the Shias that render them out of the fold of Islam such as them claiming that Imaam Mahdi disappeared into a remote cave with the original Qur’aan (which he will produce when he reappears!) and that the Qur’aan that we have with us is merely a notebook and a collection of memoirs (Naoozhu billah!) of Hadhrat Uthmaan (radhiallahu anhu) or that there are ten Juz of the original Qur’aan missing from the Qur’aan that we have which, according to them, has been tampered with and altered. They also claim that all the Sahabah (Radhiallahu Anhum) became murtad (Naoozhu billah!) with the exception of four: viz Hadhrat Ali, Hadhrat Salmaan Farsi, Hadhrat Miqdaad and Hadhrat Abu Zhar (Radhiallahu Anhum). If people hold such beliefs then Muslims should not even perform Salaatul-Janazah for them.
[see also Fataawa Mahmudiyya, Vol. 2, Pgs. 24-25; Meerut Edition].

Those Shias that hold the belief that there are 12 Imaams whose Imaamat is actually a continuation of Nabuwwat. They possess hidden qualities of Imaamat and for them Ismat (Imams being sinless) is a beautiful garb, so that they may be protected from being accused of refuting the belief of Khatm-e-Nabuwwat. Because of this type of belief too, they  are regarded to be out of the fold of Islam. They are referred to as the Imaamiyyah or Ithna Ashariyya sect.
  [Re:- Kitaabun Nawaazil Pg.51/57 Vol.2]     

Similarly, those that swear and curse Hadrat Abu Bakr Radhiallahu Anhu and Umar Radhiallahu Anhu and consider to be out of the fold of Islam.
[Re:- Fataawa Hindiyya Pg.264 Vol.2]     

In Jawaahirul-Fiqh Hadhrat Mufti Muhammed Shafi Saheb Rahmatullahi Alaih [Vol. 1, Pgs. 178-183] has given a detailed explanation of the different types of Shias that one may encounter. The gist of that discussion is that the first type are of Shias are those who deny essential and basic tenets of faith. This type of Shias are totally out of the fold of Islam which means that we should not treat them as Muslims; i.e. don’t have inter-marriages with them, don’t perform their Janaazah Salaah, don’t bury them in our Muslim Cemeteries, etc. 

The second type are those Shias who do not deny the essential and basic tenets, rather they merely aver for example that Hadhrat Ali (Radhiallahu Anhu) was the most superior of the Sahabah (Radhiallahu Anhum) and not Hadhrat Abu-Bakr (Radhiallahu Anhu). These Shias are not Kaafir but definitely Faasiq and astray. We can perform Janaazah Salaah for them, bury them in our cemeteries, etc. 

The third type are those Shias whose beliefs are not known as they do not declare them openly and prefer to conceal them. In other words, there is no certainty as to whether they deny the basic tenets of Imaan or not. With regard to this type, Hadhrat Mufti Saheb Rahmatullahi Alaih quotes his Shaikh Hadhrat Moulana Thanwi Rahmatullahi Alaih that with such people one should exercise caution; i.e. it would be preferable not to deal with them as one would deal with Muslims. 

Thus, if one is not sure of a certain Shia’s beliefs, it would be best to abstain from marrying them because they practice Taqiyya. 

Notwithstanding the above, senior scholars such as Hadrat Maulana Rasheed Ahmad Gangohi Rahmatullai Alaih have regarded marrying Shias (in a general way) as impermissible; in fact he states that it is prohibited. Hadrat Maulana writes in his Fataawa that Rasulullah Salallahu Alaihi Wasallam prohibited us from mixing and having love for those that follow their whims and desires. By us marrying them, we will be mixing with them and having love for them, therefore it will not be permissible for followers of the Ahlus Sunnah Wal Jamaa’ah to marry with the Shias. There is more caution in adopting the view of Hadrat Maulana Gangohi Rahmatullahi Alaih, hence we too in conclusion advise that one refrains from marrying Shias irrespective of the category that they belong to, particularly when there are sufficient marital partners available who fall in the category of the Ahlus Sunnah Wal Jamaa’ah.   

مناکحت روافض سے اہل سنت کو جائز نہیں  ، بلکہ ممنوع ہے شرعا ، کہ رسول اللہ صلی اللہ علیہ وسلم نے اہل ہواء سے مودت ومخالطت کو منع  فرمایا ہے ، اور مناکحت میں یہ امر موجود ہے   ، لہذا مناکحت باہم اہل سنت اور  روافض کی جائز نہیں   – باقیات فتاوی رشیدیہ ص۲۴۲