In another narration, Rasulullah (sallallahu alayhi wa sallam) said: "(Whoever commits to memory) the last ten Ayat of Surah Al-Kahf, he will be protected from (the trial of) Dajjal.''
Dajjal will appear before Qiyamah. Allah Ta’ala will give him some supernatural powers the manifestation of which will shake the faith of many people. All Prophets warned their people against him. Our Nabi (sallallahu 'alayhi wa sallam) also warned us against him and ordered us to guard ourselves from his mischief and to seek refuge of Allah from his harm.
Hazrat Ibn ‘Umar (RA) narrates : “The Messenger of Allah (sallallahu alayhi wa sallam) said: ‘Whoever reads Surah Kahf on the day of Jumu’ah (Friday), a light will emanate for him from beneath his feet to the clouds of the sky, which will be a light for him on the Day of Resurrection, and he will be forgiven (his sins) between the two Fridays.’”
It is related from Abu Sa’eed al-Khudri (RA) : “Whoever reads Surah Al-Kahf on the night of Jumu’ah (Friday), will have a light that will stretch between him and the Ancient House (the Ka’bah).” (Daarimi)
“Whoever reads Surat Al-Kahf on the day of Jumu’ah (Friday), will have a light that will shine from him from one Friday to the next.” (Bayhaqi)
The Surah 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.