Muwatta Imam Malik Book of Purity, Hadith 106

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet ﷺ said, "Fatima bint Abu Hubaysh said, 'Messenger of Allah, I never become pure - am I permitted to pray?' The Messenger of Allah ﷺ said, 'That is a vein, not menstruation. So when your period approaches, leave off from the prayer, and when its grip leaves, wash the blood from yourself and pray.' "

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، زَوْجِ النَّبِيِّ ﷺ أَنَّهَا قَالَتْ قَالَتْ فَاطِمَةُ بِنْتُ أَبِي حُبَيْشٍ يَا رَسُولَ اللَّهِ إِنِّي لاَ أَطْهُرُ أَفَأَدَعُ الصَّلاَةَ فَقَالَ لَهَا رَسُولُ اللَّهِ ﷺ " إِنَّمَا ذَلِكِ عِرْقٌ وَلَيْسَتْ بِالْحَيْضَةِ فَإِذَا أَقْبَلَتِ الْحَيْضَةُ فَاتْرُكِي الصَّلاَةَ فَإِذَا ذَهَبَ قَدْرُهَا فَاغْسِلِي الدَّمَ عَنْكِ وَصَلِّي " .