One of the special worship charities whom it executed on Friday is to read Al Kahfi's letter. Here we mention some of the shahih arguments that mention the order and its priorities.
1. From Abu Sa'id al-Khudri RA, from the Prophet (peace be upon him) said:
"Whoever reads the letter of al-Kahfi on Friday night, it was emitted with him as far as he and Jerusalem 'Atiq." (Sunan Ad-Darimi, no. 3273. Also narrated by al-Nasai and al-Hakim and was recited by al-Albani in the shahih al-Targhib wa al-Tarhib, no. 736)
2. In another history still from Abu Sa'id al-Khudri ra,
"Whoever reads al-Kahfi's letter on Friday, will be lighted for him between the two Friday." (HR. Al-Hakim: 2/368 and al-Baihaqi: 3/249. Ibnul Hajar commented on this hadith in Takhrij al-Adzkar, "Hadith hasan." He stated that this hadith is the strongest hadith of al-Kahfi's letter.
3. From Ibn Umar RA, he said: The Messenger of Allah (may peace be upon him) said,
"Whoever reads the letter of al-Kahfi on Friday, will emit light from the bottom of his feet to the sky, will explain it on the Day of Judgment, and forgive his sins between the two Friday."
Al-Mundziri said: "This hadith is narrated by Abu Bakr bin Mardawaih in his interpretation with nothing. (From the book at-Targhib wa al-Tarhib: 1/298)"
When are you reading it?
Sunnah reads the letter of al-Kahfi on Friday night or on Friday. And Friday nights have been around since the sunset on Thursday. This opportunity ends until the sun sets on Friday's day. From here it can be concluded that the opportunity to read al-Kahfi's letter is since the sunset on the Thursday of the Thursday until the sunset on Friday.
Imam al-Syafi'i rahimahullah in al-Umm stated that reading the letter of al-Kahfi could be done on the eve of Friday and his day based on his history. (Al-Umm, Imam al-Syafi'i: 1/237).
On this matter, al-Hafidzh Ibnul Hajar Rahimahullaah revealed in his practice: Thus the history of the word "day" or "night" Friday. It can be concluded that the "day" is the night. Similarly, "night" is the night of the Friday and the day. (See: Faidh al-Qadir: 6/199).
Dr Muhammad Bakar Isma'il in al-Fiqh al Wadhih min al Book wa al Sunnah states that among the practices organized to be performed at night and Friday is the reading of al-Kahfi's letter based on the above hadith. (Al-Fiqhul Wadhih minal Book was Sunnah, p. 241).
. . . The opportunity to read al-Kahfi's letter is since the sunset on the Thursday of the Thursday until the sunset on Friday. . .
Priority of reading al-kahfi letters on Friday
From some of the above histories, that the rewards prepared for those who read al-Kahfi's letter on Friday or during the day will be given light (illuminated). And this light is given on the Day of Judgment, which extends from the bottom of his foot to the sky. And this shows the length of the light given to him, as Allah Ta'ala says:
"On the day when you see the believers and women, they are light shining in front and on their right." (QS. Al-Hadid: 12)
The second reply to those who read al-Kahfi's letter on Friday is the forgiveness of sin between the two Friday. And this could be the meaning of the two Friday. Because Nurr (Light) obedience will eliminate the darkness of evil, as Allah Ta'ala says:
"Indeed, good deeds abolish (sin) of bad deeds." (QS. Huud: 114)