Ibn Abi Mulaykah reports from his maternal aunt, Fatimah bint Abi Hubaysh (may Allah be pleased with her), that she had istihadah (irregular bleeding). She came to the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), and mentioned her illness. The Prophet (peace and blessings be upon him) came in, and she (may Allah be pleased with her) said: "O Messenger of Allah! Fatimah has mentioned (such and such), that she has istihadah." The Prophet (peace and blessings be upon him) said: "Tell Fatimah: every month she should refrain from prayer for the number of days of her menstruation, according to her habit before this befell her; then she should perform one ritual bath (ghusl); then ablution for every prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1660