According to Ahl al-Sunnah, a Muslim who commits a major sin short of shirk or clear disbelief remains a believer, but one whose faith is deficient — he is a believer by his faith, a sinner (fasiq) by his major sin. His affair is under Allah's will in the Hereafter: 'Indeed, Allah does not forgive associating partners with Him, but He forgives what is less than that for whom He wills.' Even if such a person is punished in the Fire, he will not remain there forever, for anyone with an atom's weight of faith will ultimately be brought out. This is the balanced middle path between the Khawarij, who declared major sinners disbelievers, and the Murji'a, who claimed sins do not harm faith at all.
Evidence — the daleel
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Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.