Man Lā Yaḥḍuruh al-Faqīh 3, record 121 of the digital edition

Translation

Musa ibn Bakr narrated from Zurara ibn Ayan, who reported from Abu Ja'far Imam Muhammad ibn Ali Al-Baqir (a.s): He was asked about a man who had a wife and then committed fornication with her mother, her daughter, or her sister. Imam (a.s) said: "No unlawful act has ever rendered lawful acts unlawful. His wife remains lawful to him." And Imam (a.s) further said: "There is no harm if a man commits fornication with a woman and then marries her afterward. He compared this to a man who steals a date from a palm tree and then buys it later-there is no harm in doing so. It is also permissible for him to marry her mother, daughter, or sister afterward. If he is already married to the woman and then marries her mother, daughter, or sister and consummates the marriage, but later finds out the relationship, he should separate from the latter, while his first wife remains lawful to him. However, he should not approach his first wife until the womb of the woman he separated from has been cleared. If a man commits fornication with his son's wife, his father's wife, his son's concubine, or his father's concubine, this does not make them unlawful for their husbands or owners. However, if he commits such an act with a concubine while she is lawfully his, she becomes forever unlawful to his son or his father. Similarly, if a man lawfully marries a woman, she becomes forever unlawful to his son or his father."

Translation: Bab Ul Qaim Publications — published with the edition, reproduced verbatim.