(5) باب جَمْعِ الْمُسْتَحَاضَةِ بَيْنَ الصَّلاَتَيْنِ وَغُسْلِهَا إِذَا جَمَعَتْ
It was narrated from 'Aishah that a woman who suffered from Istihadah at the time of the Messenger of Allah (ﷺ) was told that it was a stubborn vein (i.e., one that would not stop bleeding). She was told to delay Zuhr and bring 'Asr forward, and to perform one Ghusl for both, and to delay Maghrib and bring 'Isha' forward, and to perform one Ghusl for both, and she would perform one Ghusl for Subh.
Reference: Sunan an-Nasa'i 360
In-book reference: Book 3, Hadith 12
English translation: Vol. 1, Book 3, Hadith 360