Does divorce occur if the husband resumes smoking after having sworn by divorce that he would not smoke at the time of the marriage contract, then he smoked and divorced his wife, then took her back during her waiting period, and did not smoke after the re-marriage?

If the husband conditioned his wife's divorce on smoking and intended a specific period, then her divorce is restricted to that period, and it does not occur otherwise, because the intention of the swearer defines his oath. However, if he intended absolute abstinence from smoking, then divorce occurs upon returning to it, and two divorces have occurred, and the oath has been fulfilled.

If the return to smoking occurs during the 'iddah (waiting period), the suspended divorce takes effect, because a revocable divorce (raj'iyyah) is subject to divorce. This is the view of the majority of scholars who consider the suspended divorce to take effect upon the occurrence of the condition it is suspended upon.

As for the view of Sheikh Al-Islam Ibn Taymiyyah, if the husband did not intend divorce but rather intended emphasis, then divorce does not occur; instead, he is required to pay expiation for breaking an oath (kaffarat yameen).

It must be noted that smoking is forbidden, and swearing by divorce is among the oaths of the wicked, and using oaths to cease sins is not a sound approach.