There is no sin great enough for a Muslim to be branded a kafir or disbeliever. Even major sins like drinking alcohol, fornication and cruelty to parents can’t take you out of the fold of Islam. Only ones disbelief can take one out of Islam. For example, if a person was to say that drinking alcohol is permissible, and denies the verses of Allah, revealed in the Quran which prohibit all intoxicants, then he is has disbelieved. He can be classed a Kafir because he has made Halal what Allah made Haram.
This clip is from the lecture Democracy In Islam by Abdur-Raheem Green.
Check out this Sinning in Islam video
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