قُلْ أَطِيعُواْ اللّهَ وَالرَّسُولَ فإِن تَوَلَّوْاْ فَإِنَّ اللّهَ لاَ يُحِبُّ الْكَافِرِينَ [3:32] Say: "Obey Allah and His Messenger": But if they turn back, Allah loveth not Kaaferin (those who reject Faith and do not believe on Allah and His messanger Mohamed and follow them) "

So after coming Quran and Prophet Mohamed any one(muslims,non-muslims) who follows anybody else then Prophet Mohamed he/she is absolute Kafeer and his/her life in this world will be precisely nothing and end with repent and not good, and in other world will he/she burn under the feet of hell dweller.
The Shia's from proudnis calling all the time Ali,Ali; Husein, Khumayni,.. To be proud on some body or making someone important then Great Allah and his messanger. It is in Islam absolute Kuffr. إِنَّ اللّهَ لاَ يُحِبُّ مَن كَانَ مُخْتَالاً فَخُوراً ....; surely Allah does not love him who is proud, boastful;[4:36]

Great Allah says in Quran 6:159

إِنَّ الَّذِينَ فَرَّقُواْ دِينَهُمْ وَكَانُواْ شِيَعاً لَّسْتَ مِنْهُمْ فِي شَيْءٍ إِنَّمَا أَمْرُهُمْ إِلَى اللّهِ ثُمَّ يُنَبِّئُهُم بِمَا كَانُواْ يَفْعَلُونَ
inna alladziina farraquu diinahum wakaanuu shyiya'an lasta minhum fii syay-in innamaa amruhum ilaa allaahi tsumma yunabbi-uhum bimaa kaanuu yaf'aluuna

[6:159] As for those who divide their religion and break up into sects, thou hast no part in them in the least: their affair is with Allah: He will in the end tell them the truth of all that they did.
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in this verse and other verses great Allah point very clear to "Shiyas". So when you tell them ehh look Great Allah does'nt talk good about Shias in Quran, they say we are not these Shias. But when you say to them hee but shias comes hunderd years after then Prophet Mohamed and you divided yourselfs from original religion of Islam as Great Allah says in Quran 6:159, they has no answear for you or they tell what the devil will tell instate of them.
Also their actions are 99% against Islam(beating, hurting theirselfs in Ashora and ,,, puting stones front of their praying or sitting, crying on Graves which prophet Mohmed forbade muslim about it, asking Ali, hussain for help which is absolute SHIRK, which makes them Kaffers, supporting Kaffirs in wars against muslims the best example is their support to Kaffir(non-muslims) in Irak,...)