Abu Dawud Book 1, Hadith Number 95.
Chapter : The quantity of water that is desirable for ablution.
Narated By Anas : The Prophet (PBUH) performed ablution with a vessel which contained two rotls (1-5 pounds) (of water) and took bath with a sa’ (of water).
Abu Dawud said: This tradition has been narrated on the authority of Anas through a different chain. This version narrates: “He performed ablution with one makkuh.” It makes no mention of two rotls.
Abu Dawud said: This tradition has also been narrated by Yahya b. Adam from Sharik. But the chain mentions Ibn Jabr b. ‘Atik instead of ‘Abd Allah b. Jabr.
Abu Dawud said: I heard Ahmad b. Hanbal say: One sa’ measures five rotls. It was the sa’ of Ibn Abi Dhib and also of the Prophet (may peace be upon him).