It was narrated from Fatimah bint Qais from Banu Asad Quraish that she came to the Prophet ﷺ and mentioned that she suffered from Istihadah. She said that he said to her: “That is a vein, so when the time of menstruation comes, stop praying, and when it goes, take your bath and wash the blood from yourself then pray.” (Sahih)