It is narrated from Hazrat Aisha that Sahla bint Suhail used to have continuous menstrual bleeding. She came to the Prophet (peace be upon him) and asked him about it. The Prophet (peace be upon him) ordered her to perform ghusl (ritual bath) at the time of every prayer. But when it became difficult for her to do so, the Prophet (peace be upon him) instructed her to combine Zuhr and Asr with one ghusl, and Maghrib and Isha with one ghusl, and to perform Fajr prayer with one ghusl.