Musnad Ahmad 1156:121

Surayj narrated to us, Abdullah—meaning Ibn Umar—narrated to us, from Salim Abu al-Nadr, from Abu Salamah ibn Abd al-Rahman, from Umm Salamah, who said: Fatima came to the Messenger of Allah, may Allah bless him and grant him peace, and said: "I am experiencing *istihada* (prolonged non-menstrual bleeding)." He said: "That is not menstruation; it is only a vein. Let her sit for the days of her menstrual cycles, then let her perform ghusl, then let her bind herself with a cloth, and let her pray."