Muwatta Malik 134

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

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, said, "Fatima bint Abu Hubaysh said, 'Messenger of Allah, I never become pure - am I permitted to pray?' The Messenger of Allah, may Allah bless him and grant him peace, 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