(Giving the Wife a Choice Between Divorce and Something Else)

The answer—and Allah is the One who grants success: What appears to me—and Allah knows best—is that divorce does not take effect, because the optioning (takhyīr) has corrupted the divorce. The clarification is that divorce here is doubtful due to the optioning, while the marriage is certain; the certain is not set aside by the doubtful. The scholars of the madhhab have stated that if a man says to his wife, “You are divorced—or not,” divorce does not occur; rather, the divorce is nullified, as in Sharḥ al-Azhār.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1