How is the ruling determined if menstruation ceases due to a temporary cause?

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If it is known that the cessation of menstruation is due to a temporary impediment such as illness, postpartum bleeding, or nursing, she must await the removal of the impediment and the return of her blood, no matter how long this takes, unless she reaches the age of menopause, at which point she observes the waiting period prescribed for women who have despaired of menstruation.