When is one required to perform ghusl for prayer upon seeing dark red discharge that tends towards brown on the sixth day of menstruation, knowing that complete purity may extend to the seventh day, and is it permissible to perform ghusl on the night of the sixth day before dawn or after it until sunrise?

Purity from menstruation is achieved by complete dryness or by the emission of the white discharge (al-qassah al-bayda'). If brown blood appears before seeing the white discharge, the woman is not considered pure; rather, she should wait for the white discharge and then perform ghusl (definition). A woman should not hasten until she sees the white discharge, as Aishah (may Allah be pleased with her) said: "Do not hasten until you see the white discharge." And whoever sees yellowish or brownish discharge after the cessation of blood flow is still considered menstruating until she sees what she is accustomed to, whether dryness or the white discharge. And for whoever is accustomed to the white discharge alone or along with dryness, and sees dryness before it, it is recommended for her to wait for the white discharge until the end of the chosen time for prayer. Ghusl becomes obligatory after the prayer time begins upon seeing the sign of purity, and it is not permissible to delay it until just before the Dhuhr adhan (definition).