"That is not menstruation, rather it is a vein. Tell her not to pray for the amount of time that her period used to last, then let her perform Ghusl and pray.' She used to perform Ghusl for every prayer. (Using translation from Nasāʾī 210)  

أَنَّ أُمَّ حَبِيبَةَ بِنْتَ جَحْشٍ كَانَتْ تُسْتَحَاضُ سَبْعَ سِنِينَ فَسَأَلْتِ النَّبِيَّ ﷺ؟ فَقَالَ «لَيْسَتْ بِالْحَيْضَةِ إِنَّمَا هُوَ عِرْقٌ فَأَمَرَهَا أَنْ تَتْرُكَ الصَّلَاةَ قَدْرَ أَقْرَائِهَا وَحَيْضَتِهَا وَتَغْتَسِلَ وَتُصَلِّي فَكَانَتْ تَغْتَسِلُ عِنْدَ كُلِّ صَلَاةٍ»  

Urwah ibn az-Zubayr said that Fatimah daughter of AbuHubaysh narrated to him that she asked the Messenger of Allah ﷺ and complained to him about the flowing of (her) blood. The Messenger of Allah ﷺ said to her: That is only (due to) a vein: look, when your menstruation comes, do not pray; and when your menstruation ends, wash yourself and then offer prayer during the period from one menstruation to another. (Using translation from Abū Dāʾūd 280)  

أَنَّهَا أَتَتْ رَسُولَ اللهِ ﷺ فَشَكَتْ إِلَيْهِ الدَّمَ فَقَالَ لَهَا رَسُولُ اللهِ ﷺ «إِنَّمَا ذَلِكَ عِرْقٌ فَانْظُرِي إِذَا أَتَاكِ قُرْؤُكِ فَلَا تُصَلِّي فَإِذَا مَرَّ قُرْؤُكِ فَتَطَهَّرِي ثُمَّ صَلِّي مَا بَيْنَ الْقُرْءِ إِلَى الْقُرْءِ»