He committed an immoral act with his wife’s daughter

First of all, and before answering your
question about the shar‘i ruling, the Muslim must always find out about
repentance and its means. So he should strive hard to find out about things
that will expiate sins and ask Allah for pardon, mercy and forgiveness. The
consequences of sin are terrible in this world and the Hereafter, but if
Allah, may He be glorified and exalted, sees that the Muslim sincerely
regrets what he has done, is determined to refrain from that sin in the
future, and is sincere in seeking forgiveness and turning to Him, then He,
may He be glorified and exalted, forgives sin, as He says (interpretation of
the meaning): “And verily, I am indeed Forgiving to him who repents,
believes (in My Oneness, and associates none in worship with Me) and does
righteous good deeds, and then remains constant in doing them, (till his
death)” [Ta-Ha 20:82].

But if he persists and is arrogant, and
continues in his sin as if nothing happened, then he will carry a burden on
the Day of Resurrection. Allah, may He be glorified and exalted, says
(interpretation of the meaning):

“And whosoever disobeys Allah and His
Messenger (Muhammad SAW), and transgresses His limits, He will cast him into
the Fire, to abide therein; and he shall have a disgraceful torment”

[an-Nisa’ 4:14]. 

What this man and this girl must do is
hasten to make up for their recklessness in committing these grave sins and
immoral actions, and seek forgiveness from Allah, may He be glorified and
exalted. That cannot be achieved except by taking all possible measures to
ensure that immoral actions do not occur again, by changing one’s place of
residence, and avoiding mixing with his wife’s daughter, and keeping away
from her altogether, so that seeing her will not prompt him to commit that
sin again. This is the responsibility of both parties, and her mother – who
is his wife – is also responsible. If they do not give due attention to the
matter, and they do not keep far away from one another, the Shaytaan will
tempt him again to fall into an even greater sin. 

With regard to the shar‘i ruling, it is
also serious. The Hanafi fuqaha’ stated that if a man touches a girl with
desire, then the mahram rulings regarding marriage immediately come into
effect,  even if no intercourse takes place. Whoever kisses a girl with
desire, her mother and daughter become haraam to him and she becomes haraam
to his sons. 

Ibn Abi Shaybah narrated in al-Musannaf
(3/479-480) with his isnaads that ‘Umar (may Allah be pleased with him)
undressed his slave woman, then one of his sons asked to marry her, and he
said: She is not permissible for you. 

It was narrated from ‘Amr ibn Shu‘ayb,
from his father, from his grandfather, that he undressed one of his slave
women, then one of his sons asked to marry her and he said: She is not
permissible for you. 

It was narrated that Ibn ‘Umar (may Allah
be pleased with him) said: If a man undresses his slave woman, and looks at
her with desire, she is not permissible for his son. 

As-Sarkhasi (may Allah have mercy on him)
said: 

We quote as evidence the reports of the
Sahaabah (may Allah be pleased with them) – and he mentioned some of the
reports quoted above – and because touching and kissing are a means that
lead to intercourse, they are regarded as foreplay leading to it, so they
have the same effect as intercourse itself in establishing the mahram
relationship, just as the marriage contract, which is a means for legitimate
intercourse, has the same effect in establishing the mahram relationship,
except in the case where the text states otherwise, namely that of a
stepdaughter. That is because the mahram relationship is based on
precautions; therefore anything that could lead to intercourse may have the
same effect with regard to the mahram relationship as intercourse itself,
and that is as a precautionary measure, even though it has no effect on
other rulings.

End quote from al-Mabsoot (4/206) 

Ibn al-Humaam (may Allah have mercy on
him) said: 

If a man touches a woman with desire, her
mother and daughter become haram for him, because touching and looking are
means that lead to intercourse, so they are regarded as having the same
effect, as a precaution.

End quote from Fath al-Qadeer
(3/2210) 

Moreover, the Hanafi fuqaha’ have ruled
that the marriage is annulled because of touching with desire in such cases,
as Ibn Nujaym (may Allah have mercy on him) said: In the case of a woman who
is observing ‘iddah following a revocable divorce (first or second talaaq),
if she allows her husband’s son to be intimate with her, or he kisses her
with desire, then she is not entitled to any maintenance, because the
separation did not occur as a result of talaaq, rather it occurred as a
result of an action on her part, which is the sin she committed.

End quote from al-Bahr ar-Raa’iq
(4/218) 

Az-Zayla‘i (may Allah have mercy on him)
said: 

Zina, touching and looking with desire
result in in-laws becoming prohibited for marriage … The Prophet (blessings
and peace of Allah be upon him) said: “Whoever touches a woman with desire”,
her mother and daughter become haraam for him. This is the view of ‘Umar,
‘Imraan ibn al-Husayn, Jaabir ibn ‘Abdullah, Ubayy ibn Ka‘b, ‘Aa’ishah, Ibn
Mas‘ood, Ibn ‘Abbaas and the majority of the Taabi‘een.

End quote from Tabyeen al-Haqaa’iq
(2/106) 

We do not deny that a number of scholars
stated that the mahram relationship only comes into effect as a consequence
of intercourse within the framework of a valid, legitimate shar‘i marriage.
Some of them said that intimacy and the like does not have any effect of
creating a mahram relationship. Others said that the mahram relationship
cannot be created, even as a result of intercourse, except within the
framework of a valid marriage. 

Shaykh ad-Dardeer al-Maaliki (may Allah
have mercy on him) said: 

It is permissible for a man who has
committed zina with a woman to marry her ascendants and descendants, and for
his father or son to marry her.

End quote from ash-Sharh al-Kabeer ma‘a
Haashiyat ad-Dasooqi (2/251) 

Ibn Hajar al-Haytami ash-Shaafa‘i (may
Allah have mercy on him) said: 

Intimate actions are not like intercourse,
according to the more correct view, because they do not require ‘iddah, so
by the same token they do not result in creation of the mahram relationship.

Tuhfat al-Muhtaaj
(7/303) 

Al-Bahooti al-Hanbali (may Allah have
mercy on him) said: 

There is no proof that the mahram
relationship is created as a result of intimacy or looking at the private
part or elsewhere, or by being alone with the person, even with desire,
because Allah, may He be exalted, says (interpretation of the meaning):
“but there is no sin on you if you have not gone in them” [an-Nisa’ 4:23].
What is meant by “going in” is intercourse. The same applies if she is the
one who did that, i.e., what is mentioned above of intimacy, looking at the
private part or elsewhere, and being alone with a man, with desire. Her
daughter does not become haram for him, because he did not have intercourse
with her mother.

End quote from Kashshaaf al-Qinaa‘
(5/71) 

This has been discussed previously, and we
stated which view is more likely to be correct. See
131569 

But no one would say, and no wise person
would accept it, that the husband should remain in that situation, exposing
himself to the risk of falling into sin and immoral deeds, without closing
the door to it. 

Would this husband be happy to be gathered
(on the Day of Resurrection) with the adulterers and adultresses, and to
receive the same punishment as them, of which the Prophet (blessings and
peace of Allah be upon him) spoke when he said: “…we came to something like
a tannoor (clay oven), in which there was shouting and voices. We looked
inside and saw naked men and women, towards whom flames came from beneath
them. When the flames reached them, they cried out” then he stated that they
were “the adulterers and adulteresses”, as is narrated in Saheeh al-Bukhaari
(7047). 

Undoubtedly, if your marriage to your wife
is not annulled, then leaving things as they are and continuing to live with
her daughter in the same house, with the possibility of being alone with
her, is one of the gravest of evils and opens wide the door to falling into
immoral deeds and incurring the wrath of the Lord, may He be glorified and
exalted. 

Your transgression of the sacred limits
set by Allah is worse than mere annulment of the marriage. 

If someone were to ask, does a wife become
haraam for her husband if he kills her daughter, the answer would be: No. 

But annulment of the marriage, or its
being haraam from the outset is one thing, and the abhorrent nature of the
crime is something else. 

So think: where are you, O slave of Allah,
and where is your religious commitment? How could you allow yourself to
drift away from religion and be overtaken by your desires?? 

If you stay in your marriage to this
woman, it is not permissible for you to continue in that immoral action.
This is quite clear. But, moreover, it is not permissible for you to stay
with the door to fitnah wide open in front of you. Rather you must keep away
from fitnah and its causes, with all means at your disposal, and you must
block every route that calls you to be tempted by this girl and to go back
to what you both did. 

What you must do is take precautions and
protect your religious commitment, not only by repenting from those
reprehensible actions, but also by closing the door to anything that could
make you go back to it. ‘Umar (may Allah be pleased with him) said: “Give up
riba and doubtful things.” Narrated by Ibn Maajah (2276); classed as saheeh
by al-Albaani. 

We ask Allah, may He be exalted, to
protect Muslim families from immoral actions, both obvious and hidden. 

And Allah knows best.