Is blood that comes down on the sixth and seventh days after the menstrual period considered menstruation or istihadah, knowing that the original period is five days and the total number of days of bleeding did not exceed fifteen days?

The blood the questioner saw after performing ghusl (ritual bath) is considered menstruation, because it occurred within a period suitable for menstruation. Therefore, she must stop praying and similar acts, and perform ghusl after it ceases. A woman's habitual period may increase or decrease, and any blood she sees during a possible menstrual period is considered menstruation. As for the purity that interrupts the menstrual period, it is a valid state of purity. If what she sees after a period of purity is yellowish or brownish discharge, it is not considered menstruation if it occurs outside her usual menstrual period.