1.There are several conditions that must be satisfied without which one can not receive the punishment of stoning:
Four just male must have witnessed the sin(excuse my language, I mean the exact act of penetrating) with their own eyes. So quoting the testimonies of four just male is not acceptable.
Their testimonies have to be exactly the same. If one of the testimonies differed from the others they would all get punished for defaming people of adultery.
All the witnesses must testify at the same court of law.
If the fornicator did not have a legal wife or husband, he/she would not be stoned to death.Instead, they would just be given a hundred lashes.
If the fornicator decided to confess to his/her sin, four confessions must be made at four different courts of law. So confessing for four times at the same court will not prove anything.
2. As you can see, proving adultery is almost impossible unless the corruption widely spread throughout the society. Can you even begin to imagine How possibly four Just people could find out about the ins and outs of this sin?
3.There are two kinds of sin:
Private sins which have nothing to do with the society. They have no negative impact on the people. For instance, drinking wine or watching porn scenes in private.
Public sins that can be seen by the people which means that they are likely to influence others by becoming commonplace or even turning into a norm!
All sins for which certain worldly punishments have been imposed, fall into the second category because the spiritual health of society has always been of crucial importance in Islam.Therefore, there would be no worldly punishment for sins as long as they did not result in others finding out about them. However, when it comes to punishments in the Day Of Judgement , there is no exception to the sins whether personal or public ones UNLESS one has repented of them.
وَ الَّذينَ إِذا فَعَلُوا فاحِشَةً أَوْ ظَلَمُوا أَنْفُسَهُمْ ذَكَرُوا اللَّهَ فَاسْتَغْفَرُوا لِذُنُوبِهِمْ وَ مَنْ يَغْفِرُ
الذُّنُوبَ إِلاَّ اللَّهُ وَ لَمْ يُصِرُّوا عَلى ما فَعَلُوا وَ هُمْ
and those who, when they commit an indecent act or
wrong themselves, remember Allah, and plead] Allah's [forgiveness for
their sins and who forgives sins except Allah? and who do not persist
in what they have committed while they know.(3:135)
أُولئِكَ جَزاؤُهُمْ مَغْفِرَةٌ مِنْ رَبِّهِمْ وَ جَنَّاتٌ تَجْري مِنْ تَحْتِهَا الْأَنْهارُ خالِدينَ فيها وَ نِعْمَ أَجْرُ
الْعامِلينَ Their reward is forgiveness from their Lord, and
gardens with streams running in them, to remain in them] forever [.
How excellent is the reward of the workers!(3:136)
This point should also be noted that we as Muslims are not entitled of possessing even our own lives. No sin can compare with Allah's mercy and compassion, no matter how big it might be.