(6) باب الْفَرْقِ بَيْنَ دَمِ الْحَيْضِ وَالاِسْتِحَاضَةِ
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."
Reference: Sunan an-Nasa'i 366
In-book reference: Book 3, Hadith 18
English translation: Vol. 1, Book 3, Hadith 366