Haram = Forbid by GOD "Allah"
I'm not sure about said issue. I'm a Muslim and I live in Malaysia.
As far of my understanding, Sunni and Shia are like two major groups in Islam.. Much like Catholic and Protestant in Christianity if I'm not mistaken.
I honestly don't know much about Shia as I'm a Sunni myself.
http://www.islamfortoday.com/shia.htm
From above link, the Shahadah of the Shia is "There is no god but Alláh, Muhammad is the Messenger of Alláh, Alí is the Friend of Alláh. The Successor of the Messenger of Alláh And his first Caliph.", am I right?
While for Sunni, the Shahadah is "There is no god but Alláh, and Muhammad is the Messenger of Alláh".
For me, once a Muslim, we belief there's only One God (Allah) and Muhammad as the Prophet. So, there should be no problem if we pray at any mosque, as we pray to the same God, and we have the same Prophet. We read the same Al-Quran. We believe in the same five Pillars
Five Pillars
- The Shahadah
- Solat (Pray) five times a day
- Fasting in Ramadhan
- Hajj in Mecca
- Zakat
Also we believe the same Six amendments..
- Believe in Allah
- Believe in angles
- Believe in Kitabullah (Holy Books)
- Believe in Prophets
- Believe in Qiamat (Judgement Day)
- Believe in Qada' and Qadar (Divine Justice)
Since we as Muslims regardless which Imam we follow (Sunni, Shia), we still abide by the above, so I don't see any problem if Sunni or Shia needs to pray at which mosque.. We will go to the same MasjidilHaram (for Hajj) and our Qiblat is the same Kaaba
Wallahua'lam Bissawab..