Sahih Muslim Book 3, Hadith Number 636.

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.

Safina reported: The Messenger of Allah (may peace be upon him) took a bath with one g’ of water because of sexual intercourse and performed ablution with one Mudd.