All of Sunnah Muslim clerics unanimously agree that a Muslim who commits major sins is still a Muslim and he is still in the fold of Islam. This is contradictory to the view of the Kharijites. This is on the ground that if a Muslim who commits major sins being accused as an infidel with the connotation that he is not a Muslim no more, then it also means that every Muslim who commits major sins is an apostate and he should be executed or killed according to traditional principle as what we see happened everywhere in Muslim area in the Middle East, in Africa, in South Asia and in some places in South East Asia.
The implication for this are that, the beneficiary of the killed person will lost the space for forgiveness and he only has the right for Qisas (an eye for an eye, a tooth for a tooth) on those who executed him and that there would be no limitation principles for crimes such as stealing, adultery and drinking alcohol. So, this opinion is obviously cancelled and not effective in Islamic view without having to bring up any evidence from primary and secondary sources no more (Wan Teh, 1987).
The Sunnah tradition maintains the view that a Muslim who commits a major sin is not an infidel and is still a Muslim. He is not a subject of eternal torments of the hereafter. This is also different to the view of Mu'tazilites that a Muslim who commits major sins would eternally being tormented in bitterness in the hereafter.
The Mu'tazilites' view on this matter is not suitable with the notion that a sinner who commits major sin is a Muslim as such it is mentioned in the Glorious Quran which means, "O you who have believed, prescribed for you is legal retribution for those murdered; the for the free, the slave for the slave, and the female for the female. But whoever overlooks from his brother anything, then there should be a suitable follow-up and payment to him with good conduct. This is an alleviation from your Lord and a mercy. But whoever transgresses after that will have a painful punishment" (Surah al-Baqarah 2:178).
The verse does not excommunicate a murderer of a Muslim from Islamic faith, but he is mentioned as a brother to the beneficiaries of the victim as an example. And the verse for sure is referring to brothers in "Islam". Evidences from the Quran, the traditions and consensus of clerics showing that adulterers, thieves, and those who falsely accuse the other with adultery were not killed but being punished according to restrictions or limitation principles. These people were not judged as apostates nor infidels (Explanation of al-Tahawi Creed; p.g 301). For restrictions or limitation principles in punishment, please make sure that everyone check the term first before throwing out words because it is a technical term in our law and the law is a distinct field of its own. Just like the British Common Law or Continental European Law, we also have our technical terms and principles. I am not sure how the Mullas there were educated but I studied the basic law from our school of jurisprudence basically the Shafi'ie school since it is the major school practiced here. Maybe there was a lack of communication among jurisprudence practitioners and judges so we face the problem like we are facing today in certain area such as in Middle East or in South Asia.
Sealed with prayers for mercy, peace and love, amin!