He agrees with the opinion of Ibn Hazm about intimacy. Is it permissible for his wife to engage in foreplay with him when he is fasting?

Firstly: 

The ruling
on emission of madhiy is different from the ruling on emission of maniy. The
most correct scholarly view is that emission of madhiy does not invalidate
the fast, whether it is from a man or a woman. The scholars’ opinions on
this issue have been mentioned in the answer to question no.
49752. 

Secondly: 

It should be
noted that it is not permissible for anyone to adopt the opinion of any
scholar on the basis of convenience, or because this opinion suits his whims
and desires. When there is a difference of scholarly opinion, what we must
do is that which Allaah has enjoined in the verse where He says
(interpretation of the meaning): 

“(And) if
you differ in anything amongst yourselves, refer it to Allaah and His
Messenger, if you believe in Allaah and in the Last Day. That is better and
more suitable for final determination”

[al-Nisa’
4:59]

It is not
permissible for anyone to say: I will follow the opinion of such and such a
scholar, and thus go against a hadeeth which is proven from the Prophet
(peace and blessings of Allaah be upon him). 

Hence Imam
al-Shaafa’i (may Allaah have mercy on him) said: The scholars are
unanimously agreed that if a Sunnah of the Prophet (peace and blessings
of Allaah be upon him) is proven, it is not permissible to forsake it for
the opinion of anyone. End quote. Madaarij al-Saalikeen (2/335). 

Once the
ruling is proven with saheeh evidence, no one’s opinion counts, no matter
who he is. 

The view
that masturbation or intimacy with one’s wife to the point of ejaculation
are among the things that invalidate the fast is the view of the majority of
scholars, including the four imams, Abu Haneefah, Maalik, al-Shaafa’i and
Ahmad. They quoted as evidence the fact that it is satisfaction of desire,
and that is forbidden to the person who is fasting, because Allaah says,
according to the hadeeth qudsi about the fasting person: “He gives up his
food, his drink and his desire for My sake.” Narrated by al-Bukhaari
(1894). 

This has
been explained in detail in the answer to questions no.
71213and 65698. 

We do not
deny that there is a difference of opinion on this issue. Ibn Hazm and
Shaykh al-Albaani (may Allaah have mercy on them) both thought that emission
of semen as the result of intimacy with one’s wife does not invalidate the
fast. If someone adopts this opinion on the basis of knowledge and follows
it on the basis of evidence, not on the basis of his whims and desires, then
there is no sin on him for that, because a person is only responsible within
the framework of his knowledge, but that is subject to the condition that he
only believes that on the basis of what evidence and scholarly opinions he
has available to him, and is not simply looking for a concession and the
easiest opinion. 

It is not
permissible for a Muslim to follow the mistakes of the scholars; if he does
that, all evil will be combined in him. Hence the scholars said: Whoever
follows a matter concerning which the scholars differed and follows the
easiest opinion is a heretic, or almost a heretic. End quote. See also the
answer to question no. 22652. 

What we
advise the questioner to do is to be content with that which the scholars
have agreed is permissible, which is intimacy in the form of touching or
kissing, without ejaculating, so as to protect his fast and fulfil his duty,
and for fear of falling into that which is haraam and invalidates the fast
according to consensus, namely intercourse. 

 And Allaah
knows best.