Musnad Ahmad 27:1028

Yazid narrated to us, Yahya informed us, from Nafi’, from Ibn ‘Umar, who said: I entered the mosque and saw the Prophet, may Allah bless him and grant him peace, with the people around him. I hurried to hear his speech, but the people dispersed before I reached him. He said once: "Before I reached them." So I asked a man among them: "What did the Messenger of Allah, may Allah bless him and grant him peace, say?" He said: "He forbade the *muzaffat* (pitch-coated vessels) and the *duba’* (gourd vessels)."