What is the ruling on yellowish discharge if it continues after the menstrual period and purity is not observed until after 15 days, or rarely less, or if it continues until the next period, and when does prayer become obligatory in these cases?

If the duration of bleeding and yellowish discharge exceeds 15 days, the woman is considered to be in a state of istihadah (non-menstrual vaginal bleeding). In this case, she should refer to her previous menstrual habit, and any duration beyond that is considered istihadah. If the woman does not have a previous habit, then red blood is considered menstruation (hayd), and if it stops and she sees yellowish discharge, she considers it istihadah and performs the actions of a woman in istihadah.