What is the ruling on one who swore an oath of divorce upon his wife (You are divorced if you smoke hashish or cigarettes from today until the end of this year), then wished to return to smoking cigarettes only?

Smoking is forbidden (haram). If the smoker consumes hashish or other drugs, the prohibition is even more severe. Your statement, "I cannot quit," is a significant error. Rather, you must promptly repent and seek assistance from specialized clinics.

Regarding the oath: 1. Ruling on conditional divorce: The majority of scholars rule that divorce takes effect if the condition is met. Some, however, are of the view that if the intention was to threaten, then an expiation for breaking an oath (kaffarat yamin) is required. 2. Breaching the oath by smoking cigarettes: If you intended only to quit hashish cigarettes, then you do not breach the oath unless you smoke them. If the reason for your oath was the specific harms of hashish, and you used something else that does not carry these harms, then you do not breach the oath. If you had no specific intention or reason for the oath, then merely consuming anything encompassed by the wording of the oath will cause you to breach it.