What is required of a woman who has stopped menstruating after experiencing post-natal bleeding (Nifas)?

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If a woman knows the cessation of her post-natal bleeding (nifas), she must continue the ritual cleansing period (Istibra') until her menstruation returns. If her menstruation returns, she must observe the Istibra' of a menstruating woman by means of one full menstrual cycle. However, if she becomes one who has despaired of menstruating (Aaisah), she must observe the Istibra' prescribed for women who have despaired of menstruation.