Is it obligatory to complete the fast when a small amount of blood appears before Fajr without being certain that it is menstruation?

The madhhabs (schools of thought) of the scholars regarding the minimum duration of menstruation considered Islamically valid have been detailed previously: According to the Hanafis, the minimum is three days and nights. According to the Hanbalis and Shafi'is, it is one day and one night. And according to the Malikis, it is a single drop. The preponderant opinion is that of the majority of scholars. Therefore, slight bleeding before Fajr is not considered menstruation, and you must continue fasting until the bleeding persists for a duration considered Islamically valid.