Surah 2. Al-Baqara, Ayah 187

Lit., "and seek that which God has ordained for you": an obvious stress on the God-willed nature of sexual life.

Lit., "the white line of dawn from the black line [of night]". According to all Arab philologists, the "black line" (al-khayt al-aswad) signifies "the blackness of night" (Lane II, 831); and the expression al-khaytan ("the two lines" or "streaks") denotes "day and night" (Lisan al-'Arab).

It was the practice of the Prophet to spend several days and nights during Ramadan - and occasionally also at other times - in the mosque, devoting himself to prayer and meditation to the exclusion of all worldly activities; and since he advised his followers as well to do this from time to time, seclusion in a mosque for the sake of meditation, called i'tikaf, has become a recognized - though optional - mode of devotion among Muslims, especially during the last ten days of Ramadan.

Lit., "deceived" or "defrauded yourselves [in this respect]": an allusion to the idea prevalent among the early Muslims, before the revelation of this verse, that during the period of fasting all sexual intercourse should be avoided, even at night-time, when eating and drinking are allowed (Razi). The above verse removed this misconception.

 “Garment” (libâs) is a metaphor for comfort, chastity, and protection.

 Initially, intimate relations during the night of Ramaḍân were not permissible. Since some Muslims could not resist not having intercourse with their spouses, this verse was revealed allowing intimacy during the nights preceding the fast.

 This implies offspring.

Men and women are each other's garments: i.e., they are for mutual support, mutual comfort, and mutual protection, fitting into each other as a garment fits the body. A garment also is both for show and concealment. The question of sex is always delicate to handle: here we are told that even in such matters a clear, open, and honest course is better than fraud or self-deception. The sex instinct is classed with eating and drinking, an animal thing to be restrained, but not to be ashamed of. The three things are prohibited during the fast by day, but permitted after the fast is broken at night till the next fast commences.

There is difference of opinion as to the exact meaning of this. I would connect this as a parallel clause with the clause "eat and drink", which follows, all three being governed by "until the white thread", etc. That is, all three things must stop when the fast begins again in the early morning. Or it may mean: What is permitted is well enough, but seek the higher things ordained for you.

Those in touch with Nature know the beautiful effects of early dawn. First appear thin white indefinable streaks of light in the east; then a dark zone supervenes; followed by a beautiful pinkish white zone clearly defined from the dark. This is the true dawn; after that the fast begins.

Till the night appears: From the actual practice of the Holy Apostle, this is rightly interpreted to mean: "Till sunset."

Retreat to the Mosques by night after the fast is broken is specially recommended towards the end of Ramadham, so that all carnal temptations may be avoided.

I construe these limits as applying to the whole of the regulations about fasts.