Sahih Muslim Book 3, Hadith Number 637.

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 that Abd Bakr, the Companion of the Messenger of Allah (way peace be upon him), observed: The Messenger of Allah (may peace be upon him) took a bath with one Sa’ of water and performed ablution with one Mudd (of water); and in the Hadith narrated by Ibn Hujr the words are: One Mudd sufficed for his (Holy Prophet’s) ablution. And Ibn Hujr said that (his Shaikh) Isma’il was much advanced in age, and it was because of this that he could not fully rely on him for this tradition.