Musannaf Ibn Abi Shayba 1:1363

Safwan ibn Isa narrated to us, from Muhammad ibn Uthman al-Makhzumi, who said: I asked Salim and al-Qasim about the woman experiencing istihada (prolonged non-menstrual bleeding). One of them said: She waits for the days of her menstrual cycle, and when the days of her menstrual cycle have passed, she performs ghusl (ritual bath) and prays. The other said: She performs ghusl from Dhuhr to Dhuhr.