Is it permissible to spy on the husband to ensure he is free from infectious diseases as a preventative measure against harm, especially since previous spying on him confirmed suspicions of his committing adultery?

Accusing a Muslim of indecency is a serious matter, and Islamic law stipulates four witnesses to prove it. It is not permissible for a wife to pry into her husband's private affairs or spy on him, and speaking about such matters without proof constitutes slander (qadhf) which necessitates a prescribed punishment (hadd). As for illness, it is permissible to seek divorce to avert harm if there is a strong presumption, based on clear indications, that the husband has an infectious disease.