Is it permissible for neighbors to inform a husband that they have seen a strange man enter his house several times in his absence, due to his work, and they suspect his wife's infidelity?

One must not seek out the faults of others or indulge in suspicions. If one does so, repentance and seeking forgiveness are required. If a person is certain that someone has committed a sin: 1. If they commit it openly, there is no impediment to disclosing their affair so that people may avoid them and be wary of them. 2. If they do not commit it openly, then it is obligatory to conceal their affair and avoid exposing them, while it is possible to advise and warn them.

Based on this, it is not permissible to inform the husband of what was seen unless the wife committed the sin openly, while attempting to warn him in a way that does not lead to accusing her of adultery or causing a rift.