The ruling on marrying a wife's sister after her death

Question:
If a man marries a woman and she bears him children, and then this first wife passes away, is it permissible for him, according to the Shari'ah, to marry her younger or older sister so that she may be kind to her sister's children or those under his care?

Answer:
Yes, there is no harm. He may marry her sister if she died, or if he divorced her and she completed her waiting period. There is nothing wrong with it. He may marry her sister, or her paternal aunt, or her maternal aunt. Praise be to Allah. What is forbidden is combining them in marriage. But if she died or was divorced, he is not combining them. If she died or was divorced and completed her waiting period, he may take her sister, her paternal aunt, or her maternal aunt, so that she may be kind to the first wife's children. Yes.

The presenter: May Allah reward you with good.

The Shaykh: That is, provided there is no impediment between them due to milk kinship.

The presenter: Yes, may Allah reward you, O Shaykh.