Musnad Ahmad 32:626

Aswad ibn Amir narrated to us, Zuhayr narrated to us, from al-Mukhtar ibn Fulful, who said: I asked Anas about the vessels for nabidh (fermented drink). He said: The Messenger of Allah, peace and blessings of Allah be upon him, forbade that which is coated with pitch (zift) from anything. He said: And the Prophet of Allah, peace and blessings of Allah be upon him, said to me: "It is the pitch-coated vessel."