What is the known reason for the Almighty's saying: "And do not marry those [women] whom your fathers married," especially the phrase "min an-nisa' (from among women)"?

The verse prohibits the marriage of sons to women married by their fathers. It was revealed because of the practice of the people of pre-Islamic ignorance (Jahiliyyah) who used to marry their fathers' wives. The Almighty's saying: "of women" implies generalization, so the prohibition is not limited to wives but also includes slave-women. Thus, the father's wife is prohibited, as is anyone he married by right of ownership (milk al-yamin).