al-Qasim ibn Muhammad القاسم بن محمد بن أبي بكر الصديق · The Book of Menstruation and Istihadah

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.

"I said to the Prophet (ﷺ) that I was suffering from Istihadah. He said: 'Do not pray during the days of your period, then perform Ghusl and delay Zuhr and bring Maghrib and bring 'Isha' forward and pray them together, and perform Ghusl for Fajr."

"The Messenger of Allah (ﷺ) said: 'Give me the mat from the MAsjid.' She said: 'I am menstruating.' The Messenger of Allah (ﷺ) said: 'Your menstruation is not in your hand.'"