What is the ruling when dark blood appears between two instances of red blood, and the red blood segment's duration is insufficient to be considered a period of purity (less than one day, according to one narration)?
Chapter on Menstruation
Al-Mughni
Book of Purification
Primary text
If the duration of the red blood segment is insufficient to be deemed a period of purity, such as a very small amount or less than a day according to one narration, it is attached to the two blood flows between which it occurred. This is because if the blood flow had been interrupted, it would not have been ruled a period of purity; therefore, if the blood is flowing, it is more appropriate to include it in the menstrual flow. If a woman sees one day of dark blood, then one day of red blood, then another day of dark blood, followed by red blood exceeding the limit, the dark bloods are aggregated to form the menstruation, making her period two days, and the remaining blood is istihada.
Supporting text
If the period of purity is not considered valid for less than a day, then in a specific scenario involving alternating short periods of black and red blood, the initial three days are deemed menstruation, and subsequent flow is istihada. If the dark blood segment is short (half a day) followed by continuous red flow exceeding the limit, the entire dark blood flow and the initial half-day are considered menstruation.