Virtues of reciting Surah al-Kahf on Friday
There are sahih ahadith from the Prophet (peace and blessings of Allah be upon him) concerning the virtues of reciting Surah al-Kahf during the day or night of Jumu’ah (Friday). These include:
 From Abu Sa’id al-Khudri, who said: “Whoever reads Surat al-Kahf on the night of Jumu’ah, will have a light that will stretch between him and the Ka’bah.” (Narrated by al-Darimi, 3407. This hadith was classed as sahih by Shaykh al-Albani in Sahih al-Jami’, 6471)
 Another hadith narrates: “Whoever reads Surat 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-Hakim, 2/399; al-Bayhaqi, 3/249)
 Ibn ‘Umar (may Allah be pleased with him) said: “The Messenger of Allah (peace and blessings of Allah be upon him) said: ‘Whoever reads Surat al-Kahf on the day of Jumu’ah, a light will shine for him from beneath his feet to the clouds of the sky, which will shine for him on the Day of Resurrection, and he will be forgiven (his sins) between the two Fridays.’”
When to read Surat al-Kahf on Friday?
Surat al-Kahf may be read during the night or on 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 surah extends from sunset on Thursday to sunset on Friday.
Imām Bukhāri and Imām Muslim have recorded from al-Barā’, may Allah be pleased with him, that he said: “A man read sūrah al-Kahf, and in the house was a steed which began to shy; so he [the man] looked and there was a fog or cloud which had enveloped him. He mentioned that to the Prophet ﷺ (who) said: Recite O so-and-so, for it was tranquillity descending because of the Qur’ān.
Surah al Kahf as protection from the Dajjal
A ḥadīth about preserving (ḥifẓ) ten verses from the beginning of sūrah al-Kahf is ṣahīh, Imam Muslim has extracted it in his ṣahīh [his compilation of authenticated narrations] from Abu al-Dardā’, may Allah be pleased with him, from the Prophet ﷺ [who] said: “Whosoever preserves ten verses from the beginning of sūrah al-Kahf is protected from the the trial of al-Dajjāl”.