Why did the prophets warn their nations against the Dajjal, and when will he emerge?

The greatest tribulation on Earth is the tribulation of the Dajjal (Antichrist), and all messengers have warned against him. His name is derived from "dajl" (deception) due to his great camouflage. He is one of the signs of the Hour, but the time of his emergence is unknown. He will emerge from the East, from Khorasan, then head towards Medina, and he will be followed by seventy thousand Jews from Isfahan. One must remain steadfast upon his appearance and keep away from him, for he misleads people with his specious arguments until they follow him.