Musnad Ahmad 32:2056

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Abdullah ibn ‘Abdullah ibn Jabr, who said: I heard Anas ibn Malik saying: The Messenger of Allah (may Allah bless him and grant him peace) used to perform ghusl with five makkuks, and he used to perform wudu with one makkuk.