Sahih al-Bukhari Book 86, Hadith 79
The Prophet (ﷺ) said, "Avoid the seven great destructive sins." They (the people!) asked, "O Allah's
Apostle! What are they?" He said, "To join partners in worship with Allah; to practice sorcery; to kill
the life which Allah has forbidden except for a just cause (according to Islamic law); to eat up usury
(Riba), to eat up the property of an orphan; to give one's back to the enemy and fleeing from the
battle-field at the time of fighting and to accuse chaste women who never even think of anything
touching chastity and are good believers."
Lian was mentioned in the presence of the Prophet, `Asim bin Adi said a statement about it, and when he left, a man from his tribe came to him complaining that he had seen a man with his wife. `Asim said, "I have been put to trial only because of my statement." So he took the man to the Prophet (ﷺ) and the man told him about the incident. The man (husband) was of yellow complexion, thin, and of lank hair, while the man whom he had accused of having been with his wife, was reddish brown with fat thick legs and fat body. The Prophet (ﷺ) said, "O Allah! Reveal the truth." Later on the lady delivered a child resembling the man whom the husband had accused of having been with her. So the Prophet (ﷺ) made them take the oath of Lian. A man said to Ibn `Abbas in the gathering, "Was that the same lady about whom the Prophet (ﷺ) said, "If I were to stone any lady (for committing illegal sexual intercourse) to death without witnesses, I would have stoned that lade to death?" Ibn `Abbas said, "No, that was another lady who used to behave in such a suspicious way among the Muslims that one might accuse her of committing illegal sexual intercourse."
I heard Abu-l-Qasim (the Prophet) saying, "If somebody slanders his slave and the slave is free from what he says, he will be flogged on the Day of Resurrection unless the slave is really as he has described him."