Sunan an-Nasa'i 366
سنن النسائي#366SahihIt 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 3:18