Musnad Ahmad 27:305

Waki’ narrated to us, Hammad bin Salamah narrated to us, from ‘Asim bin al-Mundhir, from ‘Ubaydullah bin ‘Abdullah bin ‘Umar, from his father, who said: The Messenger of Allah (ﷺ) said: "When the water is the amount of two qullahs or three, nothing makes it impure." Waki’ said: "Meaning by the qullah, the jar."