Women having the habit of duration are of two types:
498. A woman whose duration of Hayz in two consecutive months is same but the commencing times differ. In such circumstances her habit of duration will be the number of days during which blood is seen. For example, if blood is seen from the 1st to the 5th of the 1st month and from the 11th to the 15th of the 2nd month her duration habit will be 5 days.
A woman who sees blood in two consecutive months for 3 or more days, and then it stops for a day or two before it starts again, though the time of commencement of blood varies in the 2nd month from that of the 1st, her duration habit will be the number of days during which blood is seen, provided that the total number of the bleeding and Pak days does not exceed ten and that the duration period in both the months remains equal.
As a measure of precaution, in the intervening days, she will do all that is obligatory upon a lady who is Pak, and also refrain from all those acts which a Haaez is forbidden to do. For example, if during the 1st month she sees blood from the 1st to the 3rd day and then it stops for 2 days and then sees again for 3 days, and in the 2nd month she sees it from the 11th to the 13th and then it stops for 2 days and then sees it her duration habit will be six days.
And if the duration in two consecutive months is not constant, like, if she sees blood for 8 days in the first month and for 4 days in the next, then a pause, and again bleeding starts making the total 8 days by including the intervening days, then such a woman cannot be classified as woman with fixed duration. She will be Mudhtariba, whose rules will be discussed later.
499. If a woman with the fixed habit of duration sees blood for less or more days than her habitual duration, but the number of those days does not exceed 10 she should treat them as Hayz. And if it exceeds 10 days and the nature of blood remains same throughout, then she will calculate her habitual duration from the day bleeding began, and treat it as Hayz. But if the nature of blood changes, with some days showing signs of Hayz and others showing signs of Istihaza, then there can be three possibilities:
if the number of days in which blood shows signs of Hayz tallies with the habitual duration, then she will take those days as of Hayz, and the rest as Istihaza.
if the number of days in which blood shows signs of Hayz exceeds her habitual duration, then she will take her habitual duration as Hayz, and the rest as Istihaza.
if the number of days in which blood shows signs of Hayz is less than her habitual duration, she will add some days to complete her duration and take that period as Hayz, and treat the rest of the days as of Istihaza.