It was narrated from 'Amr bin Az-Zubair that Fatimah bint Abi Hubaish told him that she came to the Messenger of Allah and complained to him about (continual) bleeding. The Messenger of Allah said to her:"That is a vein. Look and when your period comes, do not pray, and when your period ends, then purify yourself and pray during the time between one period and the next

English translation · Sunan an-Nasa'i