(A) Is sex forbidden at any time in marriage ?
Yes, by considering the discomfort for the women during the monthly periods, Islam has forbidden both the husband and the wife from engaging in sexual intercourse during menstruation.
The Qur'an says:
They ask you about menstruation. Say: "Menstruation is a discomfort (for women). Do not establish sexual relations with them during the menses and do not approach them (sexually) until the blood stops. Then when they have cleansed themselves, you go into them as Allah has commanded you." (2:222)
According to the shari'ah, the duration of the monthly period is between three to ten days. If the bleeding was for less than three days, it is not menstruation; if it is for more than ten days, then it is menstruation for ten days and then it is counted as istihazah, irregular bleeding during which sex is permitted. (For further details, see my Ritual Ablutions for Women.)
The prohibition of sex during the periods is limited strictly to sexual intercourse; other intimate contact (with the exception of the vagina and anus) is allowed. However, it is better not to play with her body between the navel and the knees.
If a person who is engaged in sexual intercourse with his wife discovers that her period has begun, then he should immediately withdraw from her.
It is clear from the verse mentioned above (until the blood stops) that once the blood has stopped, intercourse becomes lawful even if the woman has not performed the major ritual ablution (ghusl). But on the basis of the subsequent sentence (then when they have cleansed themselves...), most mujtahids say that it is better to refrain from intercourse till she performs the ghusl or, at least, washes her private parts. (Wasa'il, vol. 1, p. 576)
Sexual intercourse is also not allowed during the post-natal bleeding (10 days), during daytime in the month of Ramadhan, and when a person is in ihram during the pilgrimage to Mecca. At all other times, sexual intercourse is allowed.
(B) Is it discouraged (makruh) to have sex at any time or on any day ?
There are certain ahadith which say that sexual intercourse during some days and at some times is makruh, but not haram.
These days and times are as follows:
i. during frightful natural occurrences, e.g., eclipse, hurricane, earthquake;
ii . from sunset till maghrib;
ii. from dawn till sunrise;
iii. the last three nights of lunar months;
iv. eve of the 15th of every lunar month;
v. eve of 10th Zil-hijjah;
vii. after becoming junub.
Some of these are self-explanatory: I don't think any one would be in the mood for sexual intercourse during a hurricane or earthquake. The second and third examples are of the prayer times; obviously, a Muslim is expected to spend that time in meditation and prayer. One must remember, firstly, that it is makruh, not haram, to have sexual intercourse at these times. Secondly, the ahadith for such issues have been accepted on basis of the qa'idatu 't-tasamuh mentioned earlier. Thirdly, the reasons given for this karahat are mostly about possible deformity of a child conceived at that time. By looking at these reasons, I am inclined to restrict this karahat only in cases of couples who plan to have children, and not extend it to those who practice birth control.
I would therefore advise the readers to be considerate to your spouse and not to put him or her in unnecessary tension; It your spouse is very sensitive about these makruh days then try to accommodate your likes and dislikes accordingly. Mutual understanding is the key.
(C) Are there days and times when sexual intercourse is recommended?
Yes we have certain ahadith which say that it is better to have sexual intercourse at these times:
i. Sunday night;
ii. Monday night;
iii. Wednesday night;
iv. Thursday noon;
v. Thursday night;
vi. Friday evening;
vii. whenever the wife wants to have sex.
Thursday and Friday are weekends in the Islamic calendar!
(A) Are there times when it is obligatory (wajib) to have sexual intercourse ?
Yes! It is wajib on man to have sex with his wife at least once in every four months; this is considered as one of the conjugal rights of the wife. This obligation stays in force unless there is a valid excuse or the wife waives her right.