عَنْ عَائِشَةَ رَضِيَ اَللَّهُ عَنْهَا
قَالَتْ: «إِنَّ فَاطِمَةَ بِنْتَ أَبِي حُبَيْشٍ كَانَتْ تُسْتَحَاضُ، فَقَالَ رَسُولُ اَللَّهِ (صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ) «إِنَّ دَمَ اَلْحَيْضِ دَمٌ أَسْوَدُ يُعْرَفُ، فَإِذَا كَانَ ذَلِكَ فَأَمْسِكِي مِنَ اَلصَّلَاةِ، فَإِذَا كَانَ اَلْآخَرُ فَتَوَضَّئِي، وَصَلِّي»
Fatima bint Abu Hubaish used to have a prolonged flow of blood (Istihadah) and so the Messenger of Allah (sallallahu alayhi wa sallam)· told her, “If it is the blood of menstruation it will be dark (almost black) and recognizable (by women). If it is that, then leave the prayer. If it is other than that, then make ablution and pray.”
Bulugh al-Maram 166, Book 1, The Book of Purification, Hadith 166. 1 min read