Istihadha (Hadith No. 228)
Fatima bint Abi Hubaish came to the Prophet and said, “O Allah’s Apostle I get persistent bleeding from the uterus and do not become clean. Shall I give up my prayers?” Allah’s Apostle replied, “No, because it is from a blood vessel and not the menses. So when your real menses begins give up your prayers and when it has finished wash off the blood (take a bath) and offer your prayers.” Hisham (the sub narrator) narrated that his father had also said, (the Prophet told her): “Perform ablution for every prayer till the time of the next period comes.”
How to differentiate between period blood and the blood coming from the vessel? Period blood is deeper in color and has a certain smell to it. And it lasts a few days (according to your routine). A woman experiencing this should not leave Salah the whole month. She should leave Salah only during the days of her period. And for the rest of the days, she should clean her clothes and make fresh wudu before each Salah.