Tafsir of Al-Kahf 18:25-26

{And they remained in their cave} He means their remaining therein alive, with a veil cast over their ears for this duration. This is an explanation of what was summarized in His saying: {So We cast a veil over their ears in the cave for a number of years}.

{Say, "Allah is most knowing of how long they remained."} The meaning is: He is more knowing than those who differed regarding the duration of their stay, and the truth is what Allah has informed you of. It is narrated from Qatadah that this is a recounting of the speech of the People of the Book, and {Say, "Allah is most knowing"} is a refutation of them. In the codex of ‘Abd Allah, it is written: "And they said, 'They remained...'"

{Three hundred years} "Years" (sinin) is an explanatory apposition (‘atf bayan) to "three hundred." It is recited as thalathumi’at sinin (genitive construction), placing the plural in the position of the singular for the specifier (tamyiz), similar to His saying: {the greatest in [their] works of loss}. In the reading of Ubayy, it is thalathumi’at sanah (three hundred years).

{And added nine} Meaning: nine years, because what precedes it indicates it. Al-Hasan read it as tis’an with a fatha.

{To Him belongs the unseen of the heavens and the earth.} He then mentions His exclusivity regarding what is hidden in the heavens and the earth, and what is concealed therein of the states of their inhabitants and others, and that He alone is the Knower of it.

He brought forth that which indicates wonder at His perception of the audible and the visible, to signify that His matter in perception is beyond the limits of the perception of those who hear and see. This is because He perceives the most subtle and smallest of things just as He perceives the largest in volume and the densest in mass, and He perceives the inner depths just as He perceives the outward appearances.

{They have not, besides Him, any protector} The pronoun refers to the inhabitants of the heavens and the earth. {Any protector}—that is, one who manages their affairs.

{And He does not share His legislation with anyone.} Meaning: in His decree. Al-Hasan read it as wa-la tushrik (do not associate), with a ta and a jussive mood, as a prohibition.

{And recite what has been revealed to you of the Book of your Lord. There is no changer of His words, and never will you find in other than Him a refuge.}