Purification (Kitab Al-Taharah)
Dawud :: Book 1 : Hadith 294
Narrated Aisha, Ummul Mu'minin:
A woman had a prolonged flow of blood in the time of the Apostle of Allah (peace_be_upon_him). She was commanded to advance the afternoon prayer and delay the noon prayer, and to take a bath for them only once; and to delay the sunset prayer and advance the night prayer and to take a bath only once for them; and to take a bath separately for the dawn prayer.
I (Shu'bah) asked AbdurRahman: (Is it) from the Prophet (peace_be_upon_him)? I do not report to you anything except from the Prophet (peace_be_upon_him).