The Prophet ﷺ said, "Whoever hears of the Dajjal should keep far away from him, for a man may come to him thinking himself a believer, yet because of the doubts that accompany him, the Dajjal will keep working on him until he follows him."
حدثنا يحيى بن سعيد حدثنا هشام بن حسان حدثنا حميد بن هلال عن أبي الدهماء
عن النبي ﷺ قال من سمع بالدجال فلينأ منه فإن الرجل يأتيه وهو يحسب أنه مؤمن فلا يزال به لما معه من الشبه حتى يتبعه
Its isnad is sahih. It is found in Abu Dawud 2/431, no. 4319, and Hakim graded it sahih in 4/531, and Dhahabi remained silent about it.