Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.127.
Section : Recitation of Surah al-Kahf.
It is preferred to recite surah al-Kahf during the day and night of Jumu’ah.
Abu Sa’id al-Khudri reports that the Prophet said: “Whoever recites Surah al-Kahf on Jumu’ah will have illumination from the light from one Jumu’ah to the next.” This is related by an-Nasa’i, al-Baihaqi, and alHakim.
Ibn ‘Umar reports that the Prophet said: “Whoever recites Surah al-Kahf on Jumu’ah will be blessed with a light that will rise from underneath his feet to the peak of the sky. This will be a light for him on the Day of Resurrection, and he will be forgiven for what is between the Jumu’ah [and the next] Jumu’ah.” This is related by Ibn Mardwwiyah with a faultless chain.