It is narrated from Sayyidah Asma' bint Umays (may Allah be pleased with her) (in one narration: Asma' bint Abi Bakr; the narration of Abu Ali is more correct) that she said: I said: O Messenger of Allah (peace and blessings be upon him)! Fatimah bint Abi Hubaysh (may Allah be pleased with her) has had istihadah (irregular bleeding) for such and such a length of time, and she has not prayed. He (peace and blessings be upon him) said: "Subhan Allah (Glory be to Allah)! This is from Satan. Tell her to sit in a tub." She sat in it until we saw yellowness on top of the water. He (peace and blessings be upon him) said: "She should perform one ritual bath (ghusl) for Zuhr and Asr, then one ghusl for Maghrib and Isha, then one ghusl for Fajr, and perform ablution in between."
In the narration of Abu Ali it is: She should sit in a tub, and when she sees yellowness on top of the water she should perform ghusl.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1658