Does stoning of adulterer in Islam apply for the man who is widow or divorced? or it is only for married man?

Adultery [zina] is prohibited in all faiths
In Islamic law, stoning [rajm] is the penalty prescribed for a spouse who commits adultery. Indeed, adultery is one of the foulest crimes to the extent that it is abhorred by all faiths as well as by people of discernment.
Evil consequences of adultery
- It includes encroaching upon the rights of spouses.
- It causes lineage confusion.
- It dissolves family ties.
- Abolishes parental feelings of kindness, sympathy, care and self-denial towards their children which reach the degree of sacrificing one's self and comfort. Such matters cannot be achieved unless the feeling of parenthood fills parents' hearts, which in turn cannot be felt unless they are certain deep inside that these children are their biological offspring.
In order to fight such an abominable crime, Islam has prescribed this deterring penalty—i.e. stoning for a married person and whipping [Jald] for the unmarried. However, some people [ignorantly] consider this penalty a repugnant offense for which Islam is to be blamed. They consequently remove Islam from the scope of civilized humanity and designate it as barbaric.
Evidence on stoning and whipping in primary texts
The Qur`an
Allah Almighty says,
The [unmarried] woman or [unmarried] man found guilty of sexual intercourse - lash each one of them with a hundred lashes, and do not be taken by pity for them in the religion of Allah, if you should believe in Allah and the Last Day. And let a group of the believers witness their punishment. (An-Nur, 2).
The Sunnah
The Messenger of Allah (peace and blessings be upon him and his family) said, "It is not permissible to spill the blood of a Muslim except in three [instances]: a married person who commits adultery, a life for a life, and one who forsakes his religion and separates from the community" [Muslim].
Islam is a comprehensive and cohesive religion
How Islam protects its followers from committing adultery
Islam prohibits men from gazing at non-mahram women. The Prophet (pbuh) said, “A gaze is like a poisoned arrow of Satan; whoever refrains from it out of fear from Allah, he will be rewarded (by Allah) with belief its sweetness he will find within his heart” [Recorded by Al-Hakim in Al-Mustadark].
Likewise, Allah commanded women not to show their adornment to anyone except their husbands or mahrams [non-marriageable kin]. Allah Almighty says,
O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments. (Al-Ahzab, 59).
And tell the believing women to reduce their gaze. (An-Nur, 31).
He also commands men not to be alone in private with non-mahram women. The Prophet (pbuh) said, "No man is alone with a woman [who is unlawful for him] in private, but Satan is their third partner."
The Prophet prohibited men from touching women who are unlawful for them as per his words, "It is better that you be struck on your head with a needle and bleed than to touch a woman who is unlawful to you." (Recorded by al-Tabarani).
Other than what has been previously mentioned, Islam managed to instill conscience in men and women alike.
In Islam, marriage is the only lawful means for attaining sexual pleasure
Islam urged youths to marry to release their sexual desire in a lawful way. The Prophet (pbuh) said, "O young people, whoever of you possesses the means to get married, let him do so for verily, it helps you to lower your gaze and preserves your chastity. And whoever is unable to marry [due to financial inability] let him fast, for it controls sexual desire" [Bukhari].
Allah made it lawful [halal] for men to have one, two, three or up to four wives as long as he possess the financial means and ability to treat them fairly.
Islam commands parents and guardians not to ask for exorbitant dowries for their daughters. The Messenger of Allah (pbuh) said, “If there comes to you one with whose religion and manners you are satisfied, then give your daughter to him in marriage, for if you do not do so, fitnah and mischief will prevail on earth” [Recorded by IbnMajah].
The rich as well are commanded to help young people in covering their marriage expenses. The just Caliph 'Umar IbnAbd Al-Aziz (may Allah be pleased with him) helped young men and women to marry from the Muslims' treasury.
All of the above are some of the features that Islam has set down to ease fulfilling one's physical needs in a lawful way.
How Islam curtails the abominable act of adultery
In fact, the abominable act of adultery does not occur in the Muslim community, which is characterized by virtue, except after great malicious tactics from both parties involved. Despite this, Islam has set very strict conditions for applying the penalty of adultery on the adulterer or adulteress. If these conditions are not met together, the penalty, whether stoning or whipping, is not applied. These conditions include:
- The presence of four just witnesses who testify that they have seen the partners engage in intercourse as a husband and wife — a matter which can hardly ever be witnessed by anyone. This illustrates that Islamic law has designated this penalty not for the act itself but for committing it in public in order to deter those who are immoral from spreading this abominable act within the community.
- It is established in Islamic law that penalties are waived by doubt. This means that the penalty is waived by any doubt concerning the testimony of any of the witnesses that tips the balance in favor of the accused. The Prophet (pbuh) said, "Waive penalties if any doubt occurs therein" [Recorded by Al-Tirmidhi].
- Islamic law prescribed 80 lashes for whoever falsely accuses a married woman and does not produce 4 witnesses to testify that they saw her engage in intercourse. Allah Almighty says,
And those who accuse chaste women and then do not produce four witnesses - lash them with eighty lashes and do not accept from them testimony ever after. And those are the defiantly disobedient. [An-Nur, 4].
- Islamic law urges its followers to conceal the sins of Muslims and not to publicly announce immoral acts even if they have been already committed. The Prophet (pbuh) said to a man who came to testify on witnessing a man and woman committing adultery, "Shouldn't you have covered them with your garment?" Allah Almighty says,
Indeed, those who like that immorality should be spread [or publicized] among those who have believed will have a painful punishment in this world and the Hereafter. And Allah knows and you do not know. [An-Nur, 19].
Verily, a person for whom all these [above mentioned] means have been made possible and who still dares to commit such an abominable crime, and whose matter becomes known by the public when he is witnessed by such a number of people, is a corrupt and aberrant person who leads other astray. Consequently, if a violator is not severed from the community or disciplined, he poses a threat to the entire society. Not only this, but the consequence of the penalty is repentance from this sin.
Through research, one finds that this penalty was seldom applied except in few cases throughout Islamic history. There is no harm in this as long as it provides the community safety and stability.
Like the Qur'an, the Sunnah was revealed to the Prophet (pbuh) and it explains the Qur`an. Allah Almighty says,
And We revealed to you the message that you may make clear to the people what was sent down to them and that they might give thought. [An-Nahl, 44].
The Qur`an is revealed for recitation unlike the Sunnah.
However, this does not mean that it is obligatory to stone every adulterer. This is because establishing the crime of adultery according to legal proves of the shari'ah is very hard and cannot be attained in most cases. This legal penalty prescribed in shari'ah is rather for deterrence than actual application. Applying this penalty in our time is being hindered by many requirements relating to the uprightness of the witnesses. Moreover, our time is marked by doubtful matters and the like issues which hinder applying this penalty.
Allah Almighty knows best.