Fatimah bint Abu Hubaysh said, "Messenger of Allah, I do not become pure. Should I abandon the prayer?"The Messenger of Allah ﷺ replied, "That is only a vein, not menstruation. When menstruation comes, leave off the prayer, and when its usual duration has passed, wash the blood from yourself and pray."
قالت فاطمة بنت أبي حبيش: يا رسول الله! إني لا أطهر أفأدع الصلاة؟ فقال لها رسول الله ﷺ: إنما ذلك عرق، وليست بالحيضة؛ فإذا أقبلت الحيضة فاتركي الصلاة، فإذا ذهب قدرها فاغسلي عنك الدم وصلي.
Malik narrated it in Tahara (104) from Hisham bin Urwa, from his father, from Ayesha, and by his route Bukhari in Hayd (306) and Muslim in Hayd (333) narrated it. Bukhari also narrated it briefly in Hayd (331), with the wording, "When menstruation comes, leave prayer, and when it departs, wash the blood off yourself and pray." This is an abridgment of the story of Fatimah mentioned above.