Musnad Ahmad 1156:244

I read to Abd al-Rahman: Malik, from Nafi’, from Sulayman ibn Yasar, from Umm Salamah, the wife of the Prophet, may Allah bless him and grant him peace, that a woman used to have blood flowing [continuously] during the time of the Messenger of Allah, may Allah bless him and grant him peace. Umm Salamah, the wife of the Prophet, may Allah bless him and grant him peace, asked for a legal opinion for her from the Prophet, may Allah bless him and grant him peace. He said: "Let her observe the number of nights and days that she used to menstruate during the month before what has afflicted her afflicted her, and let her leave the prayer for that amount of the month. When she reaches that [time], let her perform ghusl, then bind herself with a cloth, then pray."