It was narrated that 'Aishah said:
"Fatimah bint Abi Hubaish said to the Messenger of Allah (ﷺ): 'O Messenger of Allah (ﷺ), I do not become pure. Should I stop praying? The Messenger of Allah (ﷺ) said: 'That is a vein and is not menstruation. When your period comes, stop praying, and when the same amount of time as your regular period has passed, then wash the blood from yourself and pray.'"
English reference: Vol. 1, Book 1, Hadith 219
Arabic reference: Book 1, Hadith 220