Is a woman obligated to verify the onset of menstruation at its designated time by inserting a piece of tissue or cotton, or is merely seeing it sufficient, and what is the evidence for this from the Quran and Sunnah?

A woman is not considered to be menstruating unless she sees menstrual blood that has become visible in the outer vulva. As for the transfer of menses or the presence of blood inside the vagina, the ruling of menstruation is not established by it, and there is no need to search for it as long as it has not become apparent and visible. The fundamental principle is that a woman, before menstruation, has the status of a ritually pure person.