those who declare their wives to be their mothers and thereafter go back on what they have said shall free a slave before they may touch each other. that is what you are exhorted to do. allah is fully aware of all your deeds.
والذين يظاهرون من نسائهم ثم يعودون لما قالوا فتحرير رقبة من قبل أن يتماسا ذلكم توعظون به والله بما تعملون خبير