The ruling on the father's wife and the grandfather's wife as mahram (a relative one may not marry)
Machine translationRead the Arabic original
Question:
Welcome.
Answer:
Your father's wife or your grandfather's wife is a mahram (a relative one may not marry) to you, whether she is your father's or your grandfather's second, third, or fourth wife, whether your grandfather is on your father's side or your mother's side. You are a mahram to her. Welcome.[An-Nisa 4:22]. The term "father" includes the father and the grandfather, including the grandfather on the father's side and the grandfather on the mother's side, provided they have fathers.
Welcome.
Answer:
Your father's wife or your grandfather's wife is a mahram (a relative one may not marry) to you, whether she is your father's or your grandfather's second, third, or fourth wife, whether your grandfather is on your father's side or your mother's side. You are a mahram to her. Welcome.
And do not marry those [women] whom your fathers married
وَلَا تَنكِحُوا مَا نَكَحَ آبَاؤُكُم مِّنَ النِّسَاءِ
Source
قناة «العلامة الدكتور صالح الفوزان»، لقاءات مفتوحة-04-لقاء مفتوح - الدمام - 13-8-1420 هـ — youtube.com (57:27)
The Arabic text is a machine transcription of the audio recording.