this one, or this one, or this one, whenever he wishes—at night, by day, or at any time. It may also be said: however he wishes, so long as he does not have intercourse in the anus; and wherever he wishes.
His statement, “If he marries a virgin, he stays with her for seven [nights], then resumes the rotation; and [if he marries] a previously married woman, [he stays with her] for three,” refers to the initial allocation of turns. If he marries a virgin, he stays with her for seven—that is, seven nights, since nights are the basis for this arrangement. This is why he did not say “seven [days],” but rather “seven [nights],” for the night is the basis of the division. He then returns to his wives, spending the eighth night with the first wife.
The evidence is the hadith of Anas ibn Malik, may Allah be pleased with him: “It is from the sunnah that, if one marries a virgin when he already has a previously married wife, he stays with her for seven nights and then divides his time equally.” (1)
As for the rationale: first, a man’s desire for a virgin is generally greater than his desire for a previously married woman, so the Lawgiver grants him a period until he is satisfied.
Second, a virgin is more shy than a previously married woman. This period was therefore prescribed so that she may feel at ease, her apprehension may disappear, and she may become accustomed to her husband. This is part of the wisdom of the Sacred Law.
Included in the ruling of a virgin is a woman whose virginity was lost without intercourse, such as through a fall or the like.
As for a previously married woman, she has become accustomed to men and therefore does not need additional days to put her at ease. For this reason, the Lawgiver assigned her three days. This is why the author said, “and [if he marries] a previously married woman, [he stays with her] for three.”