The days of purity between each menstrual cycle are called tuhr. In the same way the number of menstruation (hayd) days can change from month to month, the length of a woman’s tuhr may vary as well. For example, one month there can be 25 days of tuhr and the next 32 days. As long as the purity falls within the parameters allotted in Islamic law (Shari’ah), there is no reason for concern.
The Fiqh of It
The most important principle when it comes to purity is the idea of a 15-day separator – this means that there must be a minimum of 15 complete days between two instances of bleeding. As far as the maximum – there is none, and a woman’s tuhr can extend indefinitely.
While the word tuhr is a collective term for any type of purity, the Shari’ah breaks down the concept into further subcategories. These definitions come into play when a woman experiences irregular bleeding (istihada) or has a tuhr of less than 15 days and reviews her bleeding record to determine the ruling that applies to her situation.
Tuhr Tam (Complete Purity)
A purity of 15 days or more, regardless of whether it is sahih or fasid.
Tuhr Sahih (Valid Purity)
A purity that is 15 days or more, is not mixed with any bleeding, and is preceded and followed by valid bleeding.
Tuhr Naqis (Incomplete Purity)
A purity less than 15 days.
Tuhr Mutakhallil (Intervening/Mixed Purity)
A purity less than 15 days between two instances of bleeding. This tuhr connects the blood before and after it together. Even though a woman does not see blood, these tuhr days are given the ruling of (legal) blood as they are surrounded by an insufficient purity.
Tuhr Fasid (Invalid Purity)
A purity less than 15 days; or a purity which is 15 days or more, but is mixed with blood or did not come between two valid bleedings.