Muhammad b. 'Uthman asked al-Qasim b. Muhammad about the woman who has a prolonged flow of blood. He replied:She should abandon prayer during her menstrual period, then wash and pray ; then she should wash during her menstrual period.
حَدَّثَنَا الْقَعْنَبِيُّ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي ابْنَ مُحَمَّدٍ - عَنْ مُحَمَّدِ بْنِ عُثْمَانَ، أَنَّهُ سَأَلَ الْقَاسِمَ بْنَ مُحَمَّدٍ عَنِ الْمُسْتَحَاضَةِ، فَقَالَ تَدَعُ الصَّلاَةَ أَيَّامَ أَقْرَائِهَا ثُمَّ تَغْتَسِلُ فَتُصَلِّي ثُمَّ تَغْتَسِلُ فِي الأَيَّامِ .
AbuDaud
Purification (Kitab Al-Taharah) • Hadith 303