Sahih Muslim, Chapter: The Book of Menstruation (Kitab Al-Haid)

The Messenger of Allah (may peace be upon him) took a bath from the vessel (which contained seven to eight seers, i.e. fifteen to sixteen pounds) of water And I and he (the Holy Prophet) took a bath from the same vessel. And in the hadith narrated by Sufyan the words are:" from one vessel." Qutaiba said: Al-Faraq is three Sa' (a cubic measuring of varying magnitude).