Tafsir of Az-Zukhruf 43:21

(Or have We given them a scripture before it, so they are holding fast to it?)

This is an interruption (idrab) from negating that they possess knowledge through the path of reason, to invalidating that they have any evidence from the path of transmitted tradition. Thus, the am (or) is disjunctive, not conjunctive, and it is not parallel to His saying—Exalted is He—(Did they witness...?), as some have claimed, due to the distance [between the two interpretations].

The pronoun in (before it) refers to the Quran, due to its being known from the context, or to the Messenger—upon him be peace and blessings. The sin in (holding fast) is for emphasis, not for seeking (a request); meaning: Rather, have We given them a scripture before the Quran or before the Messenger—may Allah’s peace and blessings be upon him—that speaks to the validity of what they claim, such that they are holding fast to that scripture and relying upon it?

And His saying—Majestic and Exalted is He—: