Sahih Muslim Book 3, Hadith Number 630.

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.

‘Aisha reported: I and the Messenger of Allah (may peace be upon him) took a bath from one vessel which was placed between me and him and he would get ahead of me, so that I would say: Spare (some water for) me, spare (some water for) me; and she said that they had had sexual intercourse.