When Will the Dajjal Appear?
Question

Why did the Prophets warn their people about the Dajjal when he will not emerge until the end of time? And when will the Dajjal emerge?
Praise be to Allah.The Greatest Trial: Who Is Al-Dajjal?
The greatest Fitnah (trial, tribulation) on the face of the earth since the creation of Adam until the onset of the Hour will be the Fitnah of the Dajjal, as the Prophet (peace and blessings of Allah be upon him) said. Hence there is no Prophet, from Nuh to Muhammad (may the blessings and peace of Allah be upon them all), who did not warn his people about him, as an indication of how serious his Fitnah will be.
Although Allah knows that he will not emerge until the end of time, nevertheless He commanded the Messengers to warn their people about him so that they would understand how serious the matter is.
It was narrated that the Prophet (peace and blessings of Allah be upon him) said: “If he emerges whilst I am still among you, then I will suffice you against him, otherwise each man should take care of himself, d Allah will take care of every Muslim on my behalf (and safeguard him against his evil).” (Narrated by Muslim, 5228)
The Dajjal is a serious matter, indeed he is the greatest Fitnah, as it says in the Hadith, since the creation of Adam and until the Hour begins. No wonder that he is the only one of the trials of life from which refuge is sought in prayer: “A`udhu Billah min `adhab Jahannam wa min `adhabil qabri wa min fitnatil-mahya wal-mamat wa min fitnatil-maih ad-dajjal (I seek refuge with Allah from the torment of Hell, the torment of the grave, the trials of life and death and the trial of the Dajjal).”
The word Dajjal comes from the word Dajl, which means misrepresentation or falsification, because he is a falsifier, indeed the greatest falsifier and the worst liar of all people.
When Will Ad-Dajjal Emerge?
The appearance of the Dajjal is one of the signs of the Hour, but the time of his emergence is not clearly defined, because no one knows when the Hour will be except Allah. Similarly with regard to the portents of the Hour, all we know is what has already happened (but with regard to those which have not yet happened, we do not know when they will happen).  The time of his appearance is not known, but we do know that it is one of the portents of the Hour.
Where Will Ad-Dajjal Emerge From?
With regard to the direction from which he will emerge, he will emerge from the east, from the direction of tribulation and evil, as the Prophet (peace and blessings of Allah be upon him) said: “Fitnah is here,” and he pointed towards the east. (Narrated by Al-Bukhari, 3279 and Muslim, 5167).
So the east is the source of evil and tribulation, and he will emerge from the east, from Khurasan, passing through Isfahan and entering the Arabian Peninsula from a point between Syria and Iraq, with no goal but Madinah, because there lies the Bringer of glad tidings and warnings (peace and blessings of Allah be upon him). He will want to destroy the people of Madinah, but it will be forbidden to him, as was narrated from the Prophet (peace and blessings of Allah be upon him): “At every gate thereof will be angels guarding it.” (Narrated by Al-Bukhari, 1880 and Muslim, 2449)
This man will emerge between Syria and Iraq, and seventy thousand of the Jews of Isfahan will follow him, because they are his troops. (Narrated by Muslim, 5237)
The Jews are among the most evil of the slaves of Allah, and he is the most misguided of the slaves of Allah. So they will follow him and support him, and they will be his troops, they and others who follow him. The Prophet (peace and blessings of Allah be upon him) said: “O slaves of Allah, stand firm; O slaves of Allah, stand firm.” (Narrated by Muslim, 5228)
The Prophet (peace and blessings of Allah be upon him) urged us to stand firm, because the matter is serious. And he (peace and blessings of Allah be upon him) said: “Whoever hears of the Dajjal, let him flee from him, for by Allah, a man will come to him thinking that he is a believer, then he will follow him because of the specious arguments he puts forward.” (Narrated by Abu Dawud, 3762; classed as authentic by Al-Albani in Sahih Abu Dawud)
A man will come to him and say, “He will never lead me astray and I will never be affected by him,” but he will keep producing specious arguments until he follows him – we seek refuge with Allah from that. We ask Allah to protect us with His protection. Praise be to Allah the Lord of the Worlds.
And Allah knows best.