Musannaf Ibn Abi Shayba 27:494

Al-Fadl ibn Dukayn narrated to us, from Ibn Abi Ghaniyah, from al-Hakam, from Sa’id ibn Jubayr, from Ibn ‘Abbas, from Buraydah, who said: I traveled with ‘Ali to Yemen, and I saw from him a certain harshness. When I arrived at the Messenger of Allah (may Allah bless him and grant him peace), I mentioned ‘Ali and criticized him. The face of the Messenger of Allah (may Allah bless him and grant him peace) began to change. He said: "Am I not closer to the believers than their own selves?" I said: "Yes, O Messenger of Allah." He said: "Whoever I am his master (mawla), then ‘Ali is his master (mawla)."