Musannaf Ibn Abi Shayba 5:209

10010. Ali bin Hashim narrated to us, from Ibn Abi Layla, from Abd al-Karim, from Amr bin Shu'ayb, from his father, from his grandfather, from the Prophet (peace and blessings of Allah be upon him), who said: "There is nothing (i.e., no Zakat) in less than five wasqs."