Musnad Ahmad 790:153

Yazid narrated to us, Hisham bin Hassan informed us, from Humayd bin Hilal, from Abu Dahma’ al-‘Adawi, from ‘Imran bin Husayn, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever hears of the Dajjal, let him keep away from him." He said this three times. "For a man will come to him and follow him, thinking that he is truthful, because of the doubts he brings with him."