What is the ruling regarding the deferred dowry (Mahr) if a man divorces his wife before consummation, and subsequently discovers a defect in her?

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If a man divorces his wife before consummation (dukhul) and then discovers a defect in her, he owes her half of the stipulated dowry. He has no right to reclaim this half because he accepted the obligation of paying half the dowry. This ruling is firm and established.