What is the ruling on blood discharge outside of the regular menstrual period for only one day?

If a woman experiences bleeding again after it has stopped and her menstrual period has ended, it is considered menstruation in two cases:

The first is that the total days of both bleedings and the days of purity do not exceed fifteen days, with the condition, according to the Hanbalis, that it recurs for three cycles. The Shafi'is, however, consider the habit established after one occurrence.

The second is that there is a period of purity between the two bleedings lasting fifteen days or more, and each bleeding itself is sufficient to be considered an independent menstrual period.

However, if the duration between the beginning of the first bleeding and the end of the second bleeding exceeds fifteen days, and the period of purity between them is less than fifteen days, then the renewed bleeding is considered irregular bleeding (istihadah (definition)).