Musnad Ahmad 1017:27

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, 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) sent us on a military expedition. He said: When we returned, he said: "How did you find the companionship of your companion?" He said: So I either complained about him, or someone else complained about him. He said: So I raised my head, and I was a man who kept his head bowed. He said: And behold, the face of the Prophet (peace and blessings of Allah be upon him) had turned red. He said: And he was saying: "Whoever I am his ally (wali), then Ali is his ally (wali)."