Tafsir of Az-Zukhruf 43:4

"And indeed, it is in the Mother of the Book," meaning in the Preserved Tablet, according to what a group has maintained. It is the mother of the heavenly books—that is, their origin—because all of them are derived from it. It is also said that the "Mother of the Book" is eternal knowledge. Others have said it refers to the decisive verses. The pronoun [in "it is"] refers to the Quran, or to the Book in the sense of the Surah, meaning that it is located within the decisive verses, which are the "Mother." This, as you can see, is [a specific interpretation].

The two brothers [Hamza and Al-Kisa'i] read it as "im" with a kasra on the hamza, either for the sake of following the [kasra of the] mim, or [because of the] "Book," for it is not kasra-ed in the absence of connection.

"With Us" (ladayna), meaning in Our presence.

"Exalted" (aliyyun), meaning of high status among the books due to its inimitability and its inclusion of great mysteries.

"Full of wisdom" (hakim): possessing profound wisdom, or "perfected" (muhkam) such that nothing else abrogates it, or "ruling" (hakim) over other books. Both [aliyyun and hakim] are predicates of "indeed" (inna).

Regarding "in the Mother of the Book," it is said to be related to "exalted" (aliyyun). Since the lam [of inna] has departed from its place and changed from its origin, its primacy is invalidated, so it is permissible to precede it with what is within its scope. Or, it may be a circumstantial qualifier (hal) from it, because it is a description of an indefinite noun that preceded it, or [it is a circumstantial qualifier] from its hidden pronoun. "With Us" (ladayna) is a substitute (badal) for "in the Mother of the Book," and although they differ in meaning, they are consistent in terms of the resulting implication. Or, it may be a circumstantial qualifier for it, or for the Book, as the genitive-annexed noun is in the position of a part, making its omission valid.

Perhaps the preferred view is that both adverbial phrases are in the position of a predicate for a deleted subject, and the sentence is an initiation to clarify the status of the ruling. It is as if, after explaining its characterization by the two aforementioned glorious attributes, it was said: "This is in the Mother of the Book and with Us." They did not permit them to be in the position of the predicate [for the explicit "indeed"] because of the entry of the lam into other than them. Regardless, the confirmed sentence is either a conjunction to the sentence upon which the oath was made, thus falling under its ruling, or it is an initiation confirming the exalted status of the Quran—about which the oaths informed—following the method of the parenthetical clause in the saying of the Exalted: "And indeed, it is an oath—if you only knew—great."