And do not marry those [women] whom your fathers married, except what has already occurred.1 Indeed, it was an immorality and hateful [to Allāh] and was evil as a way.
Translation: Saheeh International (English)
1 Before Islām. After the ruling was revealed by Allāh, men were required to release those women unlawful to them (e.g., a stepmother, one of two sisters, or any wives over the limit of four). The same obligation applies to one once he has accepted Islām.
Do not marry women whom your fathers married. That is forbidden, unless it happened before in the time of ignorance, in which case you will not be taken to account for it. Sons marrying the wives of their fathers is a shameful practice, a cause for earning Allah’s anger.