"Fatimah bint Abi Hubaish came to the Messenger of Allah and said: 'O Messenger of Allah! I am a woman who bleeds continuously and never becomes pure, should I give up the prayer?' He said: 'No, rather that is a vein and it is not menstruation. When the time of your period comes, leave off the prayer, and when it is over, take a bath and wash the blood from yourself and perform the prayer." This is the Hadith of Waki'. (Using translation from Ibn Mājah 621)
جَاءَتْ فَاطِمَةُ بِنْتُ أَبِي حُبَيْشٍ إِلَى رَسُولِ اللَّهِ ﷺ فَقَالَتْ يَا رَسُولَ اللَّهِ إِنِّي امْرَأَةٌ أُسْتَحَاضُ فَلَا أَطْهُرُ أَفَأَدَعُ الصَّلَاةَ؟ قَالَ «لَا إِنَّمَا ذَلِكِ عِرْقٌ فَإِذَا أَقْبَلَتِ الْحَيْضَةُ فَدَعِي الصَّلَاةَ وَإِذَا أَدْبَرَتْ فَاغْسِلِي عَنْكِ الدَّمَ وَصَلِّي»