Sahih Muslim Book 3, Hadith Number 633.

Chapter : The quantity of water that is desirable for a bath because of sexual intercourse, bathing of the male and female with one vessel in the same condition and washing of one of them with the left-over of the other.

Zainab bint Umm Salama (the wife of the Holy Prophet) reported that Umm Salama and the Messenger of Allah (may peace be upon him) took a bath from the same vessel.