أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا عَبْدَةُ، وَوَكِيعٌ، وَأَبُو مُعَاوِيَةَ قَالُوا حَدَّثَنَا هِشَامُ بْنُ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ جَاءَتْ فَاطِمَةُ بِنْتُ أَبِي حُبَيْشٍ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَتْ إِنِّي امْرَأَةٌ أُسْتَحَاضُ فَلاَ أَطْهُرُ أَفَأَدَعُ الصَّلاَةَ قَالَ ‏"‏ لاَ إِنَّمَا ذَلِكِ عِرْقٌ وَلَيْسَتْ بِالْحِيضَةِ فَإِذَا أَقْبَلَتِ الْحِيضَةُ فَدَعِي الصَّلاَةَ وَإِذَا أَدْبَرَتْ فَاغْسِلِي عَنْكِ الدَّمَ وَصَلِّي ‏"‏ ‏.‏

It was narrated that 'Aishah said: Fatimah bint Abi Hubaish came to the Messenger of Allah (PBUH) and said: "I am a woman who suffers from Istihadah and I never become pure. Should I stop praying?" He said: "No, that is a vein, it is not menstruation. When your period comes, stop praying, and when it goes, wash the blood from yourself and pray." Translation Not Available

Book Ref: Sunan An Nisai Book 3 Hadith 359
Web Ref:  Sunan An Nisai Vol 1 Book 3 Hadith 359