“Surely those who accuse chaste believing women, unaware (of the evils), are cursed in the world and the hereafter and they shall have a grievous chastisement. On the day when their tongue and their hands and their feet shall bear witness against them as to what they did.” (Surah an-Nūr 24:23-24)
"The above verses clarify that those who falsely accuse chaste men or women of adultery are cursed by Allah (S.w.T.) as long as they are alive, and in the hereafter they shall be deprived of His Divine Mercy. We should maintain our distance from such people on whom the wrath of Allah (S.w.T.) has descended and be very careful not to believe their false accusations. False accusers have to be penalised in this world according to the Islamic law. Once their testimony is proved false, they can never ever testify in a court of Islamic law".
“And those who accuse chaste women of adultery 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. Except for those who repent thereafter and reform, for indeed Allaah is Forgiving and Merciful".” [Quran 24: 2-5]
Allowing people to accuse chaste women, whether married or not, without a clear proof means that people could always make up such accusation, fearing no repercussion. This means that the Muslim community finds itself with a stained reputation. Every individual is threatened with false accusation. Every man suspects his wife, and every wife suspects her husband, and people doubt their legitimacy. In such an intolerable state of doubt and suspicion, every family is undermined. Moreover, when such accusations are frequently made, those who steer themselves away from adultery will begin to think that the crime is common in society. Thus, people begin to think about adultery in a different spirit, with its ghastly nature sounding less ghastly as a result of its frequent mention. Those who would not have contemplated it at all may begin to think of doing so, feeling that many others are doing it.
Thus, in order to protect people’s honor and their suffering from suspicion as a result of uncorroborated accusations, the Quran prescribes for false accusation a punishment that comes close to that of adultery. The punishment is flogging with 80 stripes, rejecting their testimony in any case or situation, and giving them the label of transgressors. The first part of the punishment is physical, while the second is moral. It is sufficient that the accuser is deprived of the right to testify, and considered deceitful. The third part of the punishment is a religious one. The one guilty of false accusation is following a line that deviates from that of faith. The only way to protect himself from such punishments is that the accuser should provide four witnesses who have seen the offence being committed, or three alongside him if he himself has seen it.
It is agreed upon by Muslim scholars that for adultery (or fornication) case to be authentically proven, four witnesses must simultaneously see, by their own eyes, the man's sexual organ inserted in the woman's sexual organ. Only when these four witnesses give such testimony is the accusation proved and the punishment of adultery (or fornication) is enforced on the perpetrators.
Such restrictions are set forth by Sharee'ah in order to limit to the least minimum the possibility of falsely accusing chaste women of adultery (or fornication), which leads to social and psychological troubles for the accused women. Even when such a sin –adultery (or fornication) - is committed, such restrictions laid by Sharee'ah will guarantee the suppression of the crime and prevents its spread among the people, which contaminates the morally pure Muslim community.
Tell your uncle the story innit, tell him this guy is spreading rumours and they ain't true. Then your uncle might sort him out :)
Same thing happened to prophets wife pbuh, ayesha, it's known as the story of IFK. I got a link that talks about this story if you want it.