Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 65
Narated By 'Abd Allah b. 'Umar : The Apostle of Allah (pbuh) said: When there is enough water to fill two pitchers, it does not become impure.
Abu Dawud said: Hammad b. Zaid has narrated this tradition on the authority of 'Asim (without any reference to the Prophet).