Is seeing a picture of the Antichrist (Al-Masih Ad-Dajjal) in a dream and seeking refuge from it permissible or forbidden?

What you saw has no legal ruling; rather, it is a manipulation from Satan to grieve the believer. Therefore, you must seek refuge in Allah from Satan, spit to your left three times, and turn over from the side you were lying on. Furthermore, maintaining prayers and remembrance [of Allah] is the best aid in repelling frightening visions.