Musannaf Ibn Abi Shaybah

Hazrat Uthman bin Abi Al-Aas says that if a woman sees yellowish discharge on days other than her menstrual days, and if this is one or two days more than her usual menstrual days, then she should count it as part of her menstruation. If it exceeds two days, then she should consider it as istihada (irregular bleeding). If her menstruation lasts six days and she sees blood for up to eight days, she should count it as menstruation, and if she sees blood for more than eight days, she should consider it as istihada.