Abī Tālib that the minimum duration of menstruation is two days. All these views are far-fetched, for Allah, exalted is He, says:
“And they ask you about menstruation. Say, ‘It is harm, so keep away from women during menstruation.’” [Al-Baqara: 222]
If blood could not be known to be menstrual until three days, or a day and a night, had elapsed, then the command to keep away from women would be conditional upon something whose occurrence could only be known after it had ended. That is invalid.
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As for postpartum bleeding, neither we nor most jurists prescribe a minimum duration. Abū Yūsuf held that its minimum duration is fifteen days, distinguishing it from the maximum duration of menstruation. As for its maximum duration, Mālik’s statements differ. On one occasion he said sixty days; on another, he said that women should be asked about it [and set no fixed limit. Ibn al-Mājishūn said that women should not be asked about it nowadays], because their practical experience has diminished and their knowledge is limited. Women were asked about this in earlier times and said that its maximum duration ranged from sixty to seventy days. Limiting it to sixty days is preferable, and this is al-Shāfiʿī’s position. Abū Hanīfa said that its maximum duration is forty days, and it has been said that this was the consensus of the Companions. It is reported from al-Hasan that its maximum duration is fifty days.
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As for irregular bleeding, all agree that it has neither a maximum nor a minimum duration. Success comes only through Allah.
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Concerning the Blood a Woman Sees in Her Various Circumstances
Any blood a woman sees is presumed to be menstrual blood and is accorded its rulings until it is known not to be menstrual blood—for example, when she sees it during a period of irregular bleeding, or in circumstances in which it is unlikely to be menstruation because of her youth or old age. To explain this general statement, women who experience bleeding fall into five categories: a young child who is not likely to menstruate; a young girl approaching puberty who may menstruate; [a woman who has reached puberty and is of menstruating age; an older woman who appears no longer to menstruate; and an elderly woman who is not likely to menstruate].