What is the ruling when a husband says to a woman who is currently menstruating, "If you become pure (tahir), you are divorced"?

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Divorce occurs immediately upon the first moment of purity, which is marked by the cessation of menstrual bleeding, even before performing the ritual bath (ghusl). This is explicitly stated by Ahmad, according to the narration of Ibrahim al-Harbi. The supporting evidence is derived from the statement of Allah: "And do not approach them until they become pure" (Quran 2:222), meaning until the cessation of blood, and then: "But when they have purified themselves" (Quran 2:222), meaning when they perform the ritual bath. Furthermore, she is treated as pure concerning rulings such as prayer obligation, validity of purification, and fasting, despite pending the *ghusl*, and since she is no longer menstruating, she must be considered pure as the two states (menstruation and purity) are mutually exclusive opposites.