Dajjaal is a man

Dajjaal is a man who will appear towards the end of time, and Jews will follow him. His appearance is a sign of the Last Hour, and he will bring with him immense Fitan (tests and trials) which will have an adverse effect on the Iman (of Muslims). Quite possibly many people may perish because of his Fitnah, except those whom Allah protects

From the virtues of Sooratul Kahf:

From Abu Sa'eed al-Khudri, who said: "Whoever reads Soorat al-Kahf on the night of Jumu'ah, will have a light that will stretch between him and the Ancient House (the Ka'bah)." (Narrated by al-Daarimi, 3407. This hadeeth was classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami, 6471)

(b) "Whoever reads Soorat al-Kahf on the day of Jumu'ah, will have a light that will shine from him from one Friday to the next."
(Narrated by al-Haakim, 2/399; al-Bayhaqi, 3/249. It was classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami', 6470)
The soorah may be read during the night or the day of Jumu'ah. The night of Jumu'ah starts from sunset on Thursday, and the day of Jumu'ah ends at sunset.

Therefore the time for reading this soorah extends from sunset on Thursday to sunset on Friday.

Dajjaal is a man who will appear towards the end of time, and Jews will follow him. His appearance is a sign of the Last Hour, and he will bring with him immense Fitan (tests and trials) which will have an adverse effect on the Iman (of Muslims). Quite possibly many people may perish because of his Fitnah, except those whom Allah protects.
As for his attributes, he would be a Kafir man, blind in one eye. He will seek to divert people from their religion by whatever means possible. So his Fitnah and danger will be immense. It is obligatory upon us to seek refuge in Allah from his Fitnah, as we have been commanded (to do so) by the Prophet (peace be upon him).

– Sheikh Salih Bin Fowzaan; Al-Muntaqaa Min Fatawa, vol. 2, pg. 97.

There are saheeh ahaadeeth that indicate that the Mahdi (peace be upon him) will appear at the end of time. He is one of the signs of the Hour. Among these ahaadeeth are the following:

1. Abu Sa’eed al-Khudri reported that the Messenger of Allaah (Peace & Blessings of Allaah be upon Him) said: "At the end of the time of my ummah, the Mahdi will appear. Allaah will grant him rain, the earth will bring forth its fruits, he will give a lot of money, cattle will increase and the ummah will become great. He will rule for seven or eight years. (Mustadrak al-Haakim, 4/557-558; he said: this is a hadeeth whose isnaad is saheeh, although it was not reported by al-Bukhaari and Muslim. Al-Dhahabi agreed with him, and al-Albaani said: this is a saheeh sanad, and its men are thiqaat (trustworthy), Silsilat al-ahaadeeth al-saheehah, vol. 2, p. 336, hadeeth 771)

2. ‘Ali (may Allaah be pleased with him) said: "The Messenger of Allaah (Peace & Blessings of Allaah be upon Him) said: ‘The Mahdi is one of us, a member of my family. Allaah will guide him in a single night.’" (Musnad Ahmad, 2/58, hadeeth 645, edited by Ahmad al-Shaakir, who said: its isnaad is saheeh; Sunan Ibn Maajah, 2/1367. This hadeeth was also classed as saheeh by al-Albaani in Saheeh al-Jaami’ al-Sagheer, 6735). Ibn Katheer said: "This means that Allaah will forgive him, grant him help, inspire him and guide him, when he was not like this before." (Al-Nihaayah, al-Fitan wa’l-Malaahim, 1/29; edited by Taha Zayni).

3. Abu Sa’eed al-Khudri said: "The Messenger of Allaah (Peace & Blessings of Allaah be upon Him) said: ‘The Mahdi is of my lineage, with a high forehead and a long, thin, curved nose. He will fill the earth with fairness and justice as it was filled with oppression and injustice, and he will rule for seven years.’" (Sunan Abi Dawud, Kitaab al-Mahdi, 11/375, hadeeth 4265; Mustadrak al-Haakim, 4/557; he said: this is a saheeh hadeeth according to the conditions of Muslim, although it was not reported by al-Bukhaari and Muslim. See also Saheeh al-Jaami, 6736).

4. Umm Salamah said: "I heard the Messenger of Allaah (Peace & Blessings of Allaah be upon Him) say: ‘The Mahdi is of my lineage and family, from the descendants of Faatimah.’" (Sunan Abu Dawud, 11/373; Sunan Ibn Maajah. 2/1368. Al-Albaani said that it is saheeh in Saheeh al-Jaami, 6734)

5. Jaabir (may Allaah be pleased with him) said: "The Messenger of Allaah (Peace & Blessings of Allaah be upon Him) said: ‘‘Eesaa ibn Maryam will descend, and their leader the Mahdi will say, "Come and lead us in prayer," but he will say, "No, one of them should lead them as an honour to this ummah from Allaah."’" The version narrated by Muslim says: "… Then ‘Eesaa ibn Maryam (Peace be upon him) will descend and their leader will say, ‘Come and lead us in prayer,’ but he will say, ‘No, some of you are leaders over others as an honour from Allaah to this ummah.’" (Reported by Muslim, 225)

6. Abu Sa’eed al-Khudri (may Allaah be pleased with him) said: "The Messenger of Allaah (Peace & Blessings of Allaah be upon Him) said: "He is one of us, behind whom ‘Eesaa ibn Maryam will pray." (Reported by Abi Na’eem in Akhbaar al-Mahdi. Al-Albaani said it is saheeh; see al-Jaami’ al-Sagheer, 5/219, hadeeth 5796).

7. ‘Abdullaah ibn Mas’ood reported that the Prophet (Peace & Blessings of Allaah be upon Him) said: "The world will not come to an end until the Arabs are ruled by a man from my family whose name will be the same as mine." (Musnad Ahmad, 5/199, hadeeth 3573. Another version says: "… whose name is the same as mine and whose father’s name is the same as my father’s." Sunan Abi Dawud, 11/370).

You should be aware that some liars have fabricated ahaadeeth about the Mahdi, and others have even claimed to be he, or that he belongs to a group other than Ahl al-Sunnah wa’l-Jamaa’ah. Some of these "false mahdis" have tried to deceive the slaves of Allaah for some worldly gain and to distort the picture of Islaam. Some have started movements and revolutions and gathered those people and supporters whom they were able to deceive. Then they were destroyed, and their lies and falsehood were exposed. None of this affects the belief of Ahl al-Sunnah wa’l-Jamaa’ah in the Mahdi, upon whom be peace, and that he will undoubtedly appear and rule the earth in accordance with Islamic Sharee’ah. And Allaah knows best.

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Sheikh Muhammed Salih Al-Munajjid