This is what i found on that site achtung gave:
Your apology is accepted. Striving to understand the rulings of Sharee'ah
in this and similar matters is not haraam or shameful; it is necessary.
As regards your question, anal intercourse with one's wife is a major sin,
whether it occurs at the time of menstruation or not. The Prophet
SAWS (Peace & Blessings of Allah be upon Him) cursed the one who does
this: "Cursed is the one who approaches his wife in her rectum" (Reported
by Imaam Ahmad, 2/479; see also Saheeh al-Jaami', 5865).
The Prophet SAWS (Peace & Blessings of Allah be upon Him) also
said: "The one who has intercourse with a menstruating woman, or with a
woman in her rectum, or who goes to a fortune-teller, has disbelieved in
what was revealed to Muhammad." (Reported by al-Tirmidhi, no. 1/243; see
also Saheeh al-Jaami', 5918).
In spite of the fact that many wives of sound nature refuse this, there are
some husbands who threaten their wives with divorce if they do not obey
them (in this matter), and some even deceive their wives, who are too shy
to ask scholars about it, into thinking that it is permissible. The Prophet
SAWS (Peace & Blessings of Allah be upon Him) said that a man may
approach his wife in any way he likes, from the front or the back, so long
as intercourse takes place in the place from through which a child is born.
There is no doubt that the rectum is the place from which waste matter is
expelled, not the place from which a child is born.
Another reason why some may commit this immoral act is that they enter
upon what should be a clean married life with some jaahili (ignorant)
traditions and odd practices, or with memories of scenes from indecent
movies, for which they have not repented to Allaah.
It is known that this act is forbidden even if both partners agree to it.
Mutual consent to a haraam deed does not make it halaal.
I ask Allah to bestow upon us a proper understanding of His religion and
to make us adhere to its limits, for He is the All-Hearing, the One Who
answers prayers.
Thanks for the site Achtung!
Jaawan
Till next time*K_I_S_S*©