Is it considered a sin to have intercourse with one's wife during an intermittent menstrual period that includes days of purity, given that the bleeding resumes later, and what should the woman do in this situation?

If a woman sees purity by one of its two signs, she must perform ghusl (ritual bath), and it becomes permissible for her husband to have intercourse with her. If the bleeding returns, she reverts to being a menstruating woman, abstaining from what a menstruating woman abstains from, such as prayer, fasting, and intercourse, as long as the duration of the menses and the periods of purity interspersed within it do not exceed fifteen days.

Scholars have differed concerning the purity that occurs intermittently during menstruation: is it a valid state of purity (talfiq/connecting), or is it ruled to be part of the menstruation (sahb/dragging)? According to both opinions, a woman must perform ghusl when she sees purity, and she should do what pure women do, and it is permissible for her husband to have intercourse with her.

The preferred opinion is that of talfiq (connecting).