Musnad Abu Ya'la al-Mawsili 3:367

Zuhayr narrated to us, Yahya ibn Sa'id narrated to us, Shu'bah narrated to us, he said: Mansur narrated to me, from Rib'i, he said: I heard Ali delivering a sermon, and he was saying: The Messenger of Allah (may Allah bless him and grant him peace) said: "Do not lie about me, for whoever lies about me will enter the Fire."