What is the waiting period for a woman obligated to observe 'Iddah by months when she is not capable of Quru'?

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The waiting period is measured by months for any woman who does not menstruate due to small age or menopause, provided she is not pregnant. The required term is three months. The supporting evidence is: {And those who have not menstruated yet, and those who are regular in menstruation—if you are in doubt—their waiting period is three months, and for those who have not menstruated} (Quran 65:4).