Sunan An-Nasai, Chapter: The Book of Purification

that the daughter of Abu Hubaish said: "O Messenger of Allah, I do not become pure, so should I stop praying?" He said: "No, that is a vein." Khalid said, in what I read from him,* "And it is not menstruation, so when your period comes, stop praying, and when it goes, wash the blood from yourself and pray." (Sahih) *Meaning, before Hisham, from whom he narrates it.