Is the wife responsible for knowing the ruling on a statement made by her husband, which she suspects might lead to major disbelief (kufr akbar)? And is she obligated to abstain from intercourse, fearing it might be considered adultery, if her husband's statement necessitates apostasy, or is she not bound by that, and is responsible for herself only?

A wife is not permitted to refuse her husband based on doubts, for the fundamental principle concerning a Muslim is their soundness, and one whose Islam is established with certainty cannot be deprived of it except by certainty. Therefore, she should not pay attention to such doubts and should beware of obsessive thoughts (waswasa). She should live with her husband in kindness, and if she observes anything from him that contradicts the Sacred Law, she should enjoin upon him what is good and forbid him from what is evil according to its prescribed Islamic guidelines.