If a person who has committed a sin repents sincerely, Allah will accept his repentance and expiate for his bad deeds, no matter how grave his sin is. This is indicated by a great deal of evidence in the Qur’an and Sunnah. Allah says, “Say: O My servants who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allah, verily, Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful” [Az-Zumar 39:53]
“And those who invoke not any other god along with Allah, nor kill such person as Allah has forbidden, except for just cause, nor commit illegal sexual intercourse; and whoever does this shall receive the punishment. The torment will be doubled to him on the Day of Resurrection, and he will abide therein in disgrace; Except those who repent and believe (in Islamic Monotheism), and do righteous deeds; for those, Allah will change their sins into good deeds, and Allah is Oft-Forgiving, Most Merciful” [Al-Furqan 25:68-70]
However, if a person persists in committing zina and does not repent from it, then textual evidences indicate that such a person will suffer different kinds of punishment, in this world, in the grave and in the Hereafter. We do not find any text that states that he will be deprived of al-hur al-`Iyn (houris), but some of the scholars have reached this conclusion by analogy with the warning concerning the one who dies without repenting from drinking wine, who will not drink it in the Hereafter; and the one who does not repent from wearing silk in this world, who will not wear it in the Hereafter.
Ibn al-Qayyim (may Allah have mercy on him) listed the punishments that will befall the one who commits zina, if he does not repent:
He exposes himself to missing out on the enjoyment of al-hur al-`Iyn in the blessed abode of the Garden of Eden. For Allah will punish the one who wears silk in this world by depriving him of it on the Day of Resurrection; and He will punish the one who drinks wine in this world by depriving him of it on the Day of Resurrection; so by the same token He will punish the one who enjoyed haram intimacy in this world. Indeed, everything of haram that a person enjoyed in this world, he will be deprived of its counterpart in the Hereafter.