How should the forgetful woman interpret the instruction to observe six or seven days as menses?
Chapter on Menstruation
Al-Mughni
Book of Purification
Primary text
The apparent meaning is that she is referred to her own judgment and opinion regarding what she believes is closest to her habit or the habit of women, or what most resembles menses. The Qadi mentioned this in some places.
Supporting text
In another context, the Qadi mentioned that she is given the choice between six or seven days, not as a matter of judgment, similar to the choice given for the expiation (Kaffarah) for intercourse during menses, which is between one Dinar or half a Dinar. The first interpretation is considered sounder because if she were given a free choice on the seventh day, it would imply a choice between the obligation of prayer and the prohibition thereof, which is not a choice she possesses. The expiation is a voluntary act where choice between Dinar or half Dinar is possible, although the obligatory expiation is half Dinar in both scenarios, as one cannot choose between performing and omitting an obligation. The conjunction 'or' (aw) can also indicate judgment, as in the verse {So when the conflict is past, then either grant freedom or take ransom} (Quran 47:4), where 'either' (imma) is in position similar to 'or', and the leader has no option other than to act based on what his judgment deems most appropriate.