Musannaf Ibn Abi Shayba 1:708

Ibn Fudayl narrated to us, from Yazid ibn Abi Ziyad, from Salim ibn Abi al-Ja’d, from Jabir, from the Prophet (peace and blessings of Allah be upon him), who said: "A *mudd* suffices for ablution, and a *sa’* for major ritual impurity (janabah)." A man said, "It does not suffice us, O Jabir." He replied, "It sufficed one who was better than you and had more hair."