Ruling on one who commits zina after doing the marriage contract and before consummation of the marriage

Firstly: 

If a woman commits zina before consummation of her marriage, then she is to
be treated in the same manner as a virgin with regard to the hadd
punishment, because the description of having been previously married, in
which case the hadd punishment is stoning, does not come into effect merely
with the drawing up of the marriage contract, even if the spouses have been
alone together in addition to having done the marriage contract. Rather it
is essential that vaginal intercourse should have occurred, as we have
explained in fatwa no. 120913 

The hadd punishment for an unmarried woman, if she commits zina, is one
hundred lashes. The basis for that is the verse in which Allah, may He be
exalted, says (interpretation of the meaning): “The woman and the man
guilty of illegal sexual intercourse, flog each of them with a hundred
stripes. Let not pity withhold you in their case, in a punishment prescribed
by Allah, if you believe in Allah and the Last Day. And let a party of the
believers witness their punishment.” [an-Noor 24:2]. 

To that may be added banishment for one each year; this is proven according
to the Sunnah. It was narrated that ‘Ubaadah ibn as-Saamit said: The
Messenger of Allah (blessings and peace of Allah be upon him) said: “Learn
from me, learn from me. Allah has ordained a way for them. For an unmarried
person with an unmarried person, one hundred lashes and exile for one year.
For a married person with a married person, one hundred lashes and stoning.”

Narrated by Muslim (1690), Abu Dawood (4415) and at-Tirmidhi (1434). 

This is the view of the majority of scholars, even though some of them
differed concerning that. Ibn Qudaamah (may Allah have mercy on him) stated
that there was a difference of opinion concerning that, and he quoted the
evidence of those who say that the woman is not to be banished. He said:

In addition to flogging, the zaani is to be banished for one year, according
to the majority of scholars. That was narrated from the Rightly Guided
Caliphs, and it was the view of Ubayy, Ibn Mas‘ood and Ibn ‘Umar (may Allah
be pleased with them), as well as ‘Ata’, Tawoos, ath-Thawri, Ibn Abi Layla,
ash-Shaafa‘i, Ishaaq and Abu Thawr. 

Maalik and al-Awzaa‘i said:

Only the man is to be exiled and not the woman, because the woman needs to
be guarded and protected, and because her exile will be either with or
without a mahram, and it is not permissible for her to be exiled without a
mahram, because the Prophet (blessings and peace of Allah be upon him) said:
“It is not permissible for a woman who believes in Allah and the Last Day to
travel the distance of one day and one night except with a mahram.”
Moreover, exiling her without a mahram exposes her to temptation and may be
the cause of her being neglected. However, if she is exiled with a mahram,
that is exiling someone who did not commit zina and banishing someone who
did not commit a sin, even if she is forced to give him money in return.
Doing that is adding to the punishment something that is not prescribed.

End quote from al-Mughni (9/43) 

The correct view concerning this matter is that a woman may be exiled if she
has a mahram with her, because the hadeeths that speak of exile are general
in meaning and include everyone who commits zina, whether man or woman. 

An-Nawawi said in his commentary on the hadeeth of ‘Ubaadah quoted above:
With regard to the words of the Prophet (blessings and peace of Allah be
upon him) “and he is to be banished for one year”, this gives proof for ash-Shaafa‘i
and the majority of scholars, who said that punishment for one year is
obligatory, whether the guilty party is a man or a woman.

End quote from Sharh an-Nawawi ‘ala Muslim (11/189) 

But if she does not have a mahram, then that she is not to be banished,
because banishing her in that case would be exposing her to temptation and
encouraging her to deviate. 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: She is to be
banished for one year, so long as she has a mahram, and she is to be
banished to a safe place. The fuqaha’ of the (four) madhhabs are of the view
that she is to be banished, even if she has no mahram. 

The second view is the one that is more correct, that she should not be
banished if she is on her own. That is because the purpose behind banishment
is to keep her away from temptation, but if she is exiled on her own, that
is more likely to lead to temptation and evil, because she has no one with
her to check her, and because if she is exiled without a mahram – especially
if she needs money – then she may end up selling her honour so that she can
eat and drink. 

The correct view is that if she does not have a mahram, it is not
permissible for her to be exiled. But what should we do? Some of the
scholars said that she should be taken out to a nearby town, within the
distance at which shortening prayers become permissible, and her guardian
should be instructed to keep an eye on her. But the correct view is that
there is no need for that, and she should remain in her own city. 

It was also said that she should be detained in a safe place. Detention in
this case takes the place of exile. That is because she will not get in
touch with anyone and no one will get in touch with her and this opinion
carries some weight. 

End quote from ash-Sharh al-Mumti‘ ‘ala Zaad al-Mustaqni‘ (14/237) 

Secondly: 

It is not necessary to separate a woman who committed zina and her husband,
whether she committed zina before or after consummation of the marriage,
because marriage is not rendered invalid by zina. Ibn Qudaamah (may Allah
have mercy on him) said: If a man’s wife commits zina, or her husband
commits zina, the marriage is not annulled, whether that occurred before
consummation of the marriage or afterwards, according to most of the
scholars.

End quote from al-Mughni (9/565). 

Thirdly: 

If the husband chooses to separate from his wife who committed zina before
consummation of the marriage, then he must divorce her (talaaq), and if he
divorces her then she is entitled to half of the agreed-upon mahr, because
Allah , may He be exalted, says (interpretation of the meaning): “And if
you divorce them before you have touched (had a sexual relation with) them,
and you have appointed unto them the Mahr (bridal money given by the
husbands to his wife at the time of marriage), then pay half of that (Mahr),
unless they (the women) agree to forego it, or he (the husband), in whose
hands is the marriage tie, agrees to forego and give her full appointed Mahr”
[al-Baqarah 2:237]. 

It is permissible for the husband to prevent her marrying someone else by
refusing to divorce her or consummate the marriage with her, so that she
will release herself from him by giving wealth, because Allah, may He be
exalted, says (interpretation of the meaning): “O you who believe! You
are forbidden to inherit women against their will, and you should not treat
them with harshness, that you may take away part of the Mahr you have given
them, unless they commit open illegal sexual intercourse. And live with them
honourably. If you dislike them, it may be that you dislike a thing and
Allah brings through it a great deal of good” [an-Nisa’

4:19].

The “open illegal sexual intercourse” mentioned in the verse is zina, as we
have explained in detail in fatwa no. 146100. 

And Allah knows best.