Is the father of one’s ex-husband a mahram?

Question

Praise be to Allah.

The husband’s father is considered to be a
woman’s mahram even if her husband divorces her, because Allaah says, stating who a one’s mahrams are (interpretation of the meaning):

“the wives of your sons who (spring) from
your own loins”

[al-Nisa’ 4:23]

In this case, the father-in-law becomes a mahram simply as soon as the marriage contract is
completed; if a man makes a marriage contract with a woman, then the man’s father becomes a mahram for his son’s wife, even if the marriage is not
consummated.

This is what the scholars called
al-mahaarim bi’l-musaaharah (mahrams by marriage).

The women who become mahrams through marriage
are of four types:

1 – Women married by one’s father (i.e.,
father’s wife and also grandfathers’ wives). Allaah says (interpretation of the meaning):

“And marry not women whom your fathers
married”

[al-Nisa’ 4:22]

2 – One’s wife’s mother or grandmother:

“Forbidden to you (for marriage) are… your
wives’ mothers…”

[al-Nisa’ 4:23 – interpretation of the
meaning]

3 – One’s stepdaughter (a wife’s daughter by
a previous husband). The stepdaughter is not a mahram unless the man has consummated the marriage with her mother. If he simply made a marriage
contract with her but did not consummate the marriage, then she is not a mahram, because Allaah says (interpretation of the meaning):

“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”

[al-Nisa’ 4:23 – interpretation of the
meaning]

4 – One’s son’s wife and one’s grandsons’
wives, because Allaah says (interpretation of the meaning):

“the wives of your sons who (spring) from
your own loins”

[al-Nisa’ 4:23 – interpretation of the
meaning]

From Jaami’ Ahkaam al-Nisa’ by
al-‘Adawi, 5/302

Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him) said:

Allaah says (interpretation of the meaning):

“… 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 …”

[al-Nisa’ 4:23]

These three are mahrams by marriage. The phrase “your wives’ mothers” means that it is haraam
for a man to marry the mother or grandmother of his wife, no matter how far the line of ascent reaches (i.e., great-grandmother, etc), whether
that is through the mother’s line or the father’s. She becomes his mahram as soon as the marriage contract is done.

If a man makes a marriage contract with a
woman, it becomes haraam for him to marry her mother and she becomes one of his mahrams even if the marriage with her daughter is not consummated.
If it so happens that the daughter dies or he divorces her, then he is still a mahram for her mother. If it so happens that consummation of the
marriage is delayed, then he is still a mahram to her mother; she may uncover her face in front of him and he may travel with her and be alone
with her, and there is no sin on him, because the mother and grandmother of the woman become mahrams as soon as the marriage contract is done,
because Allaah says “your wives’ mothers”, and a woman becomes a man’s wife as soon as the marriage contract is done.

The phrase “the wives of your sons who
(spring) from your own loins” means that it becomes haraam for a man to marry the wife of his son or grandson, no matter how far the line of
descent extends, as soon as the marriage contract is done. The wife of one’s son’s son (grandson) becomes a mahram to the grandfather as soon as
the marriage contract is done. Hence if a man makes a valid marriage contract with a woman, then he divorces her immediately thereafter, she
becomes a mahram for his father and grandfather, no matter how far the line of ascent reaches, because of the general meaning of the phrase, “the
wives of your sons who (spring) from your own loins”. The woman becomes permissible for her husband as soon as the marriage contract is done.

From al-Fataawa al-Jaami’ah li’l-Mar’ah
al-Muslimah, 2/591.