People who dont admit sin without witnesses = no punishment in this life, but they are still liable to punishment in the next life.
Bulugh Al Maraam hadith1035.
If any of your women are guilty of lewdness, Take the evidence of four (Reliable) witnesses from amongst you against them; and if they testify, confine them to houses until death do claim them, or Allah ordain for them some (other) way. [Quran 4:15]
Ubadah ibn Samit heard Allah's Messenger say [translation of meaning]: Allah has made a way out for them
[people locked in house/jail for life - if 4 witnesses saw them .;
also see; Tafsir.com Tafsir Ibn Kathir
Their way out =
100 lashes for never been married male and female (with the addition of male expelled for 1 year if he had never been married before.)
Rajm/Stoning for someone whose married or has been married if 4 believing witnesses saw it, or admitted to their crime, or pregnancy.
hadith 1036. Aba harairah bukhari and muslim.
Man said 4 times i did zina. Allah's Messenger asked, "are you majnun [mad?]". "no." he said. "are you married [or have u been married before]?" Yes. then he was stoned.
we learn; a mentally ill mad person who doesn't know what he's doing isn't punished, because he's not responsible for his actions (although mad people shouldn't be left in society to cause harm.) Because according to other ahadith, the pen is lifted from 3 types of people; the boy before he gets a wetdream (and the girl before her menstruation), the majnun [madman] until he gets his sanity again, and the one whose asleep until they wake up.
hadith 1037. Ibn abbas hadith.
A man said he had done a crime related to a non mahram woman.
Allah's Messenger replied like; "maybe you looked at her, or just kissed her, or touched her [these are different types of zina but not the major zina].
He did this to avoid him admitting his sin, so he could avoid punishment without explicitly mentioning he did major zina.
We learn that the judge should try to avoid taking the confession out of him and try to give him excuses. however, if he confesses - then the judge is compelled to make a decision.
hadith 1038. Umar ibn Al Khattab was giving khutbah and mentioned that he was scared because people will not follow the law of rajm [stoning the married/divorced] adulterer because it has been abrogated in recitation, although we (the companions) and the Messenger of Allah did it (stoned the married adulterer).
1039; Abu Hurairah Bukhari and Muslim.
Right hand possess (slave girl) - if she commits fornication, she should be lashed 40 (or 50, not sure - read the ahadith below) times (not 100) [because a slaves blood value is half of a free person because they are not free i.e. a free believers blood money is 100 camels or of equal value, and a slaves is 50 camels or of equal value - so the punishment is half for them too.]
Once the person has recieved a punishment expiating their sin, they cannot be admonished or reminded of their sin by anyone else, since their sin has been expiated [forgiven]. By admonishing the person or shouting at them, or reminding them of that sin is another form of punishment, and this is not allowed (because 2 separate punishments for a crime is not allowed, unless stated so in the religion.)
If the slave girl does it again, then again - she should recieve 40 (or 50, not sure) lashes.
If she does it again, sell her for a really low price since she's not worth being yours.
Hudud on 1040 hadith, narrated ali (sahih, mawquf [a sahabi statement only].
Exercise hudud punishment [like normal free person] on right handed slave if she does zina.
1041. Imran ibn Husein.
woman from Juhain pregnant from zina.
"I commit a hadd, so exercise punishment on me". she said to Allah's Messenger.
Allah's Messenger called her wali [guardian] and said to him to be good to her, and to treat her well, due to her knowledge of the great sin she had committed.
She would be stoned after she delivered the child.
On the day she was going to be stoned, Allah's messenger told his companions to cover her properly with proper clothing (fa shudat alayha i.e. properly so the clothes dont fall off) so she has covering clothing so she does not show her 'awrah [i.e. body] when she is being stoned (out of respect for her.)
After this, Allah's Messenger prayed janazah for her (the prayer when a Muslim dies.)
Umar ibn Khattab said that she is a major sinner, how can you pray for her? Allah's Messenger told that her repentance was so sincere that it would cover 70 people, or all of the people of Medinah.
This hadith shows that a major sinner is not a disbeliever (like some sects believe i.e. Khawarij) believe. When someone is given a punishment of hudud in this life, then they are not accountable for it on Judgment Day because their sin has been expiated.
1042. Jabir ibn Abdallah. Sahih.
Hudud punishments are for ALL people under islamic state. muslims and non muslims.
1043. Saeed ibn sa'd ibn ubada narrated. in Ahmad, Nasa'i, ibn Majah and its Hasan [good].
A small and weak man (who had never been married before) did zina/fornication with a slave woman. Allah's Messenger was informed by the sahabah and they explained he's a small and weak man. They implied that if he gets punished with 100 lashes, he'll be killed.
If his illness was only temporary, then the judge would wait to apply the punishment until he gets better.
But if he was ill or weak for all his life, it was permanent, then the following punishment would apply;
They got 100 palm tree branches, and hit them on the weak man in one Hit. To equal 100 lashes.
hadith 1044. Ibn Abas. sahih.
Punishment of someone who does the act of the people of Lut [Homosexuality], then the one who did it, and the one who its done to - both face death.
If someone does it to an animal, the one who does it, and the animal it's done to face death.
Allah's Messenger and abu bakr ordered 100 lashes for the non previously married fornicator, and exhile for one year [for the males who do so].
1046. Allah's Messenger cursed the men who imitate women [muhanath], and women who imitate men [mutarajila]. He ordered that they be removed from your houses (i.e. you don't live with them.)
1047. is a weak hadith, so it wasn't discussed.
1048. The last hadith of the chapter. Ibn Umar, Sahih in al Haakim.
Allah's Messenger ordered the believers to conceal their sins with Allah's veil of Mercy, and to repent.
So don't show off your sin, because if your sin is taken towards the judge/muslim leader, he will have to exercise the punishment on you.
Allah knows best.