What is the required waiting period for a free woman whose menstruation ceases without a known cause?

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If menstruation returns to a woman whose period has ceased within one year, she must revert to observing the waiting period based on menstrual cycles (Quru'). The yearly waiting period is abrogated because the menstrual cycle is the default basis, and its return invalidates the substitute ruling. This ruling is established based on the principle that a free woman observes one year if the cessation of her menses is unexplained. This is supported by the report concerning Umar, may Allah be pleased with him, who ruled that if a woman whose menses ceased after one or two periods waits nine months, and no pregnancy is established, she observes three months thereafter, totaling one year, and no dissenting opinion is known against this ruling among those who agreed with the primary view. Furthermore, the narration regarding Habban ibn Minhidh's wife, where her waiting period was deemed to require her husband's inheritance if he died within the defined period based on the consultation between Uthman, Ali, and Zayd ibn Thabit, reinforces this framework.