“This is concerning my question before abu ‘ Abd Allah (a.s.), about the case of a man whose wife divorces him in the manner of al-Khula‘ (payment for divorce); if it is permissible to propose marriage to her sister before her waiting period is complete. He (the Imam) said, ‘Since she has set herself free and there is no chance to go back, it is lawful for him to propose marriage to her sister.’ He (the narrator) has said that he (the Imam) was asked about the case of a man who had two sisters as his slave-girls. He goes to bed with one of them then he goes to bed with the other one. He (the Imam) said, ‘When he goes to bed with the other one, the first one becomes unlawful for him until the other one dies.’ I then asked, ‘What happens if he sells her?’ He (the Imam) said, ‘If he sells her because of a reason without anything in his mind about the other slave-girl, then I do not see it as harmful, but if he sells her so he can go to the first one, then it is not permissible.’”