Narrated Aisha, Ummul Mu'minin:

Sahlah daughter of Suhayl had a prolonged flow of blood. She came to the Prophet (ﷺ). He commanded her to take a bath for every prayer. When it became hard for her, he commanded her to combine the noon and afternoon prayers with one bath and the sunset and night prayer with one bath, and to take a bath (separately) for the dawn prayer. Abu Dawud said: Ibn 'Uyainah reported from 'Abd al-Rahman b. al-Qasim on the authority of his father, saying: A woman had a prolonged flow of blood. She asked the Prophet (ﷺ). He commanded her to the same effect.

حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ يَحْيَى، حَدَّثَنِي مُحَمَّدُ بْنُ سَلَمَةَ، عَنْ مُحَمَّدِ بْنِ إِسْحَاقَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْقَاسِمِ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ سَهْلَةَ بِنْتَ سُهَيْلٍ، اسْتُحِيضَتْ فَأَتَتِ النَّبِيَّ صلى الله عليه وسلم فَأَمَرَهَا أَنْ تَغْتَسِلَ عِنْدَ كُلِّ صَلاَةٍ فَلَمَّا جَهَدَهَا ذَلِكَ أَمَرَهَا أَنْ تَجْمَعَ بَيْنَ الظُّهْرِ وَالْعَصْرِ بِغُسْلٍ وَالْمَغْرِبِ وَالْعِشَاءِ بِغُسْلٍ وَتَغْتَسِلَ لِلصُّبْحِ ‏.‏ قَالَ أَبُو دَاوُدَ وَرَوَاهُ ابْنُ عُيَيْنَةَ عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْقَاسِمِ عَنْ أَبِيهِ أَنَّ امْرَأَةً اسْتُحِيضَتْ فَسَأَلَتْ رَسُولَ اللَّهِ صلى الله عليه وسلم فَأَمَرَهَا بِمَعْنَاهُ ‏.‏