It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her); she said: A woman asked the Prophet (peace and blessings be upon him), saying: I suffer from istihadah and I do not become pure; shall I leave the prayer? He (peace and blessings be upon him) said: "No, but leave the prayer for as many days and nights as you used to menstruate, then take a ritual bath (ghusl), bind yourself with a cloth, and pray."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19882