Musnad Ahmad 32:2149

Bahz narrated to us, Shu'bah narrated to us, Abdullah ibn Abdullah ibn Jabr narrated to us, that he heard Anas ibn Malik saying: "The Messenger of Allah (peace and blessings of Allah be upon him) used to perform ghusl (full ablution) with five makkuks (a measure of volume), and he would perform wudu (ablution) with one makkuk."