‘Urwa b. az-Zubair reported from Fatima daughter of Abu Hubaish that her blood kept flowing, so the Prophet (ﷺ) said to her, “When the blood of the menses comes it is black blood which can be recognised, so when that comes refrain from prayer; but when a different type comes perform ablution any pray, for it is due only to a vein.” Abu Dawud and Nasa’i transmitted it.

عَنْ عُرْوَةَ بْنِ الزُّبَيْرِ عَنْ فَاطِمَةَ بِنْتِ أَبِي حُبَيْشٍ: أَنَّهَا كَانَتْ تُسْتَحَاضُ فَقَالَ لَهَا النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: " إِذَا كَانَ دم الْحيض فَإِنَّهُ دم أسود يعرف فَأَمْسِكِي عَنِ الصَّلَاةِ فَإِذَا كَانَ الْآخَرُ فَتَوَضَّئِي وَصَلِّي فَإِنِّمَا هُوَ عِرْقٌ. رَوَاهُ أَبُو دَاوُدَ وَالنَّسَائِيّ