Answered by Shaykh Shuaib Ally
Question: Assalam alaikum,
1) Is it permissible to preemptively assume that a Muslim is a disbeliever, without clear evidence?
2) Is it permissible to reject the invitation to one’s own brother’s wedding meal due to such an assumption?
3) Are the Shia disbelievers? Are all Shia restaurants haram?
4) Is somebody who calls for demonstrations or elections a disbeliever?
Answer: Assalāmu ʿAlaykum,
I hope that you are well.
It is not permissible – nor logical – to pre-emptively consider someone who appears to be a Muslim a polytheist or disbeliever, without clear evidence of this being the case. People are dealt with based on their outward characteristics, not what a person believes about them without just cause.
It is not permissible to reject a wedding invitation of a Muslim on this assumption.
Calling for political participation is not polytheism.
Shias are Muslims, not polytheists.
It is permissible to eat the sacrifice of Muslims as well as the People of the Book (Jews and Christians). Consuming the sacrifice of any other, including polytheists, is impermissible.
Please see: What Takes a Person Out of the Fold of Islam? and: Universal Validity of Religions and the Issue of Takfir and: Is Voting Permitted?