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."  

أَنَّهُ سَأَلَ الْقَاسِمَ بْنَ مُحَمَّدٍ عَنْ رَجُلٍ طَلَّقَ امْرَأَةً إِنْ هُوَ تَزَوَّجَهَا فَقَالَ الْقَاسِمُ بْنُ مُحَمَّدٍ إِنَّ رَجُلاً جَعَلَ امْرَأَةً عَلَيْهِ كَظَهْرِ أُمِّهِ إِنْ هُوَ تَزَوَّجَهَا فَأَمَرَهُ عُمَرُ بْنُ الْخَطَّابِ إِنْ هُوَ تَزَوَّجَهَا أَنْ لاَ يَقْرَبَهَا حَتَّى يُكَفِّرَ كَفَّارَةَ الْمُتَظَاهِرِ