Musnad Ahmad 493:7

Yahya ibn Adam narrated to us, Sharik narrated to us, from Abu Ishaq, from Hubshi ibn Junadah al-Saluli, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Ali is from me and I am from him, and no one shall discharge [a duty] on my behalf except me or Ali." Sharik said: "I said to Abu Ishaq: 'Where did you hear it from him?' He said: 'In such and such a place, I do not remember it.'"