If, however, it is strongly suspected that some people are secretly engaging in such acts, on the basis of an indication pointing to this and signs that have emerged, then there are two cases.
The first is when failing to intervene would result in a violation of inviolability that could not be remedied afterward. For example, if someone whose truthfulness he trusts informs him that a man has secluded himself with another man in order to kill him, or with a woman in order to fornicate with her, then in such a situation it is permissible for him to spy, uncover the matter, and investigate, so as to prevent an irreversible violation of sacred limits and the commission of forbidden acts. Likewise, if a group of volunteers were to learn of such a matter, they would be permitted to undertake investigation and denounce it, as occurred in the incident involving al-Mughīrah ibn Shuʿbah.
A woman from Banū Hilāl, named Umm Jamīl bint Mihjan ibn al-Afqam, used to visit a man in Basra. She had a husband from Thaqīf named al-Ḥajjāj ibn ʿUbayd. When Abū Bakrah ibn Masrūḥ, Sahl ibn Maʿbad, Nāfiʿ ibn al-Ḥārith, and Ziyād ibn ʿUbayd learned of this, they lay in wait for him. When she entered upon him, they burst in on the two of them. What transpired concerning their testimony against him before ʿUmar is well-known. ʿUmar did not censure them for bursting in, although he had them receive the hadd punishment for slander when their testimony fell short.
The second case concerns something involving less cause for suspicion. In such a case, it is not permissible to spy on it or to uncover its coverings. It has been related that ʿUmar entered upon some people who were taking turns drinking and kindling fires in reed huts. He said, “I forbade you to take turns drinking, yet you did so; and I forbade you to kindle fires in reed huts, yet you did so.” They replied, “Commander of the Believers, Allah has forbidden spying, yet you spied; and He has forbidden entering without permission, yet you entered.” He said, “Two for two,” then withdrew and took no further action against them.
There are differing reports from Aḥmad concerning concealed wrongdoing that is known to him: should it be denounced? Ibn Manṣūr and ʿAbdullāh transmitted that he was asked about wrongdoing that was covered, such as a tanbūr (lute), an intoxicant, and the like. He said, “If it is covered, he should not break it.” This was further clarified in the narration of Yūsuf ibn Mūsā and Aḥmad ibn al-Ḥusayn concerning a tanbūr, an intoxicant, and the like, when it is behind a cloth and someone describes it or identifies it. He said, “If it is covered, I do not think he should break it.”