Must I make up for the day on which I broke my fast, thinking it was menstruation, only for it to become clear that it was not, or is it considered among the excusable errors?

Summary: Scholars have differed on the minimum duration of menstruation. The Madhhabs of Shafi'i and Ahmad state that it is one day and one night. If blood flows for less than that, it is considered dysfunctional bleeding (dam fasad) and does not prohibit prayer or fasting. Therefore, if the blood that the questioner experienced did not continue for a day and a night, she must make up the fast and prayers of that day. She is not sinful for not having intended it. However, if the blood continues for a day and a night after a complete purification (fifteen days) and is of the color of menstrual blood, then it is menstruation, and she should abstain from prayer and fasting for its duration.