Is the wife’s sister considered to be a mahram?

Question

Praise be to Allah.

The wife’s sister is
considered to be a “stranger” (non-mahram) to her sister’s husband, so it is
not permissible for him to look at her, or be alone with her, or to shake
hands with her. Some people think that because she is forbidden in marriage
to the husband that it is permissible to look at her and be alone with her
and shake hands with her, but this is wrong. What is meant by forbidden in
marriage here is that it is not permissible for a man to be married to a
woman and her sister at the same time; similarly it is forbidden to be
married to a woman and her paternal aunt or a woman and her maternal aunt at
the same time. The prohibition on being married to a woman and her sister at
the same time is mentioned in the Qur’aan. Allaah has stated that among the
women who are forbidden in marriage, as He says (interpretation of the
meaning):

“and two sisters in wedlock at the same time”

[al-Nisa’ 4:23]

And it is stated in the
saheeh Sunnah that it is forbidden to be married to a woman and her paternal
aunt at the same time, or to be married to a woman and her maternal aunt at
the same time. Narrated by al-Bukhaari, 4821; Muslim, 1408.

So what is forbidden is to be married to two sisters at the
same time, and the wife’s sister is not forbidden to the husband for
marriage in a permanent sense.

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was
asked about a woman who lives with her married sister and does not wear
hijab in front of her sister’s husband. She says that she is temporarily a
mahram (forbidden in marriage) to him. What is your response to that?

He replied:

This woman is confused. It is not permissible for her
sister’s husband to marry her so long as her sister is with him, so she is
forbidden in marriage to him for a certain period, not permanently. But her
understanding is mistaken because those who are forbidden in marriage for a
certain period are not mahrams.

The mahrams are those to whom marriage is permanently
forbidden either because of blood ties or for a permissible reason, namely
ties of marriage or ties created through breastfeeding. Allaah says
(interpretation of the meaning):

“And marry not women whom your fathers married, except
what has already passed; indeed it was shameful and most hateful, and an
evil way.

23. Forbidden to you (for marriage) are: your mothers,
your daughters, your sisters, your father’s sisters, your mother’s sisters,
your brother’s daughters, your sister’s daughters, your foster mothers who
gave you suck, your foster milk suckling sisters, your wives’ mothers, your
stepdaughters under your guardianship, born of your wives to whom you have
gone in — but there is no sin on you if you have not gone in them (to marry
their daughters), — the wives of your sons who (spring) from your own loins,
and two sisters in wedlock at the same time, except for what has already
passed; verily, Allaah is Oft‑Forgiving, Most Merciful”

[al-Nisa’ 4:22-23]

Allaah did not say, “And
the sisters of your wives.” What is forbidden is to be married to two
sisters at the same time.

Based on this, we say to the sister of the questioner, who
says that her sister speaks to her sister’s husband and does not wear hijab
in front of him, and says that they are temporary mahrams, that this is a
mistaken notion and is not correct. This is not the matter of being
temporary mahrams, because what is forbidden is to be married to two sisters
at the same time, as Allaah says: “and two sisters in wedlock at the same
time”. The case of the wife’s sister is not as the questioner
understands it.

Fataawa Ibn ‘Uthaymeen, 2/877.