Muwatta Malik: Divorce — If a man marries a woman whom he has made as his mother’s back, i.e. has made… (Hadith No. 1173)

Yahya related to me from Malik from Said ibn Amr ibn Sulaym az- Zuraqi that he asked al-Qasim ibn Muhammad about a man who made divorce conditional on his marrying a woman i.e. if he married her he would automatically divorce her. Al-Qasim ibn Muhammad said, "If a man marries a woman whom he has made as his mother's back, i.e. has made haram for him, Umar ibn al-Khattab ordered him not to go near her if he married her until he had done the kaffara for pronouncing dhihar

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Reference: Muwatta Malik: Divorce, Hadith No. 1173