Musannaf Ibn Abi Shayba 27:427

Abu Mu'awiyah and Waki' narrated to us, from al-A'mash, from Sa'd ibn 'Ubaydah, from Ibn Buraydah, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever I am his master (wali), then 'Ali is his master (wali)."