Musannaf Ibn Abi Shaybah 9110 — A woman whose menstruation lasts

Sayyiduna Uthman bin Abi al-As (may Allah be pleased with him) said: If a woman sees yellowish discharge outside the days of her menstruation, then if it exceeds her menstrual days by one or two days, she should count it as part of her menstruation. If it exceeds by more than two days, she should count it as istihadah (non-menstrual bleeding). If her menstruation is six days and she sees blood for eight days, she should count it as menstruation; and if she sees blood for more than eight days, she should count it as istihadah.