Being reckless with regard to zina on the grounds that the Muslim who commits sin will never stay in Hell for eternity
Question

What is your response to the one who says that so long as the Muslim has an atom’s weight of faith in his heart, he will enter Paradise even if he commits zina during his lifetime?
What do you say to the wife who betrays her husband by committing the immoral act of zina for the sake of sexual pleasure?.
Praise be to Allah.The belief of Ahl as-Sunnah wa’l-Jamaa‘ah is that those who commit major sins are subject to the will of Allah. If Allah wills, He will punish them, and if He wills, He will forgive them, and if they are punished, they will not remain in Hell forever. This is what is indicated by the mutawaatir texts of the Qur’aan and Sunnah, such as the verse in which Allah, may He be exalted, says (interpretation of the meaning):
“Verily, Allah forgives not that partners should be set up with him in worship, but He forgives except that (anything else) to whom He pleases, and whoever sets up partners with Allah in worship, he has indeed invented a tremendous sin”
[an-Nisa’ 4:48]. 
Al-Bukhaari (18) and Muslim (1709) narrated from ‘Ubaadah ibn as-Saamit that the Messenger of Allah (blessings and peace of Allah be upon him) said, when a number of his companions were around him: “Swear allegiance to me, pledging that you will not associate anything with Allah, you will not steal, you will not commit zina, you will not kill your children, you will not fabricate lies against one another, and you will not disobey in anything that is right and proper. Whoever among you fulfils that, his reward will be with Allah, and whoever does any of those things and is punished for it in this world, that will be expiation for him. Whoever does any of those things then Allaah conceals him, his case will rest with Allaah: if He wills He will forgive him and if He wills He will punish him.” So we swore allegiance to him on that basis. 
Al-Bukhaari (44) and Muslim (193) narrated from Anas that the Prophet (blessings and peace of Allah be upon him) said: “Whoever says Laa ilaaha ill-Allaah and has in his heart goodness the weight of a grain of barley will be brought out of Hell, then whoever says Laa ilaaha ill-Allaah and has in his heart goodness the weight of a grain of wheat will be brought out of Hell, then whoever says Laa ilaaha ill-Allaah and has in his heart goodness the weight of an atom (or a small ant) will be brought out of Hell.”
Abu ‘Abdullah said: Abaan narrated to us: Qataadah narrated to us: Anas narrated to us from the Prophet (blessings and peace of Allah be upon him) “faith” instead of “goodness”. 
This does not mean that we may be heedless or reckless with regard to sin. The sinner may be faced with a bad end or loss of faith. Hence one of the Salaf said: Sins are the harbingers of kufr. 
Moreover, no one takes the idea of the punishment of Hell lightly except the negligent fool who does not know what Hell is or what the punishment of Allah is, or that one dip in the Fire will make him forget the greatest pleasure in this world. 
There are reports concerning the punishment and humiliation of those who commit zina, that instil fear in the heart and mind and would stop anyone thinking of zina. These reports include the following: 
Al-Bukhaari (1386) narrated that Samurah ibn Jundub said: When the Prophet (blessings and peace of Allah be upon him) had prayed, he would turn to us and say: “Who among you saw a dream last night?” If anyone had seen a dream, he would tell him and say whatever Allah willed. One day he said: “Did any of you see a dream last night?” We said: No. He said: “But last night I dreamt that two men came to me and they took me by the hand and led me out to the holy land. … Then we moved on to a hole like a tannoor (a kind of oven) that was narrow at the top and wide at the bottom. A fire was lit underneath it, and when it came close they rose up until they almost came out, and when it died down they went back into it. In it were naked men and women. I said: Who are these? They said: Move on. So we moved on.” 
According to another report narrated by al-Bukhaari (7047): “… So we went on, and came to something like a tannoor (a kind of oven).  – I [the narrator] think he said: In it there was much noise and voices. We looked into it and saw naked men and women. A flame of fire was reaching them from underneath, and when it reached them, they cried out loudly. I said to them, ‘Who are these?’ They said to me, ‘Move on, move on.’ … ‘As for the naked men and women whom you saw in a structure that resembled an oven, they are the adulterers and adulteresses.’”  
And he said: “When a man commits zina, faith departs from him and hovers like a cloud over him, then when he stops that, faith returns to him.”
Narrated by Abu Dawood (4690), at-Tirmidhi (2625). Classed as saheeh by al-Albaani in Saheeh Abi Dawood. 
See also the answer to question no. 159349 
Then it may be said here to the one who has a heart: what kind of believer is this who is content to let the most precious thing he has depart from him, namely faith, when he does not know whether Allah will restore it to him as it was or take it away from him, in return for a moment of pleasure that will soon pass? 
If a woman betrays her husband, she has combined adultery, wrongdoing and treachery towards her husband, all of which are grave major sins. How does she know that she will be able to repent or that Allah will accept her repentance? Indeed she does not know whether she will be able to die as a believer or not. We ask Allah to keep us safe and sound. 
Because zina is so abhorrent and is so grave a sin, Allah has made the hadd punishment for the previously married person who commits zina stoning to death. 
We ask Allah to keep us safe and to save us and protect us and you and all the Muslims from these sins. 
And Allah knows best.