What is the ruling regarding a husband who swore to his wife, saying: "If you smoke cigarettes again, then you are forbidden to me as my mother is forbidden to me," and then his wife smelled cigarette smoke on his clothes?

The presence of cigarette odor on the husband's clothes is not conclusive proof of his smoking, and therefore does not establish his breaking of the oath he swore. The statement uttered by the husband is a conditional declaration of ẓihār dependent on his smoking cigarettes. Ẓihār does not take effect unless he actually smokes, and it is permissible to make ẓihār conditional. Ẓihār takes effect upon the husband's smoking cigarettes, and it becomes forbidden for him to have intercourse with his wife before performing the expiation for ẓihār, which is mentioned in Surat Al-Mujadilah: freeing a slave, or fasting for two consecutive months, or feeding sixty needy persons.