Tafsir of Al-Anbiya' 21:65

(Then they were overturned upon their heads): The root meaning of al-naks (overturning) is to flip a thing so that its top becomes its bottom. Mentioning the "head" is not superfluous; it serves as an emphasis or it may be considered an instance of tajrid (abstraction). Sometimes, naks is used linguistically for the absolute flipping of a thing from one state to another, and the head is mentioned to provide a vivid image and to emphasize vilification.

Al-Zamakhshari, according to what is in al-Kashf, mentioned three aspects regarding the intended meaning here:

The First: It is the regression from a sound, upright line of reasoning—where they acknowledged the injustice done to their own souls—to a corrupt line of reasoning in deeming the worship of these idols permissible, despite acknowledging that their condition falls short of even that of animals, let alone their being in the position of divinity. Thus, the meaning of (You have surely known that these do not speak) is: "It is not hidden from us, nor from you, O rebuker, that they do not speak; we only took them as gods while knowing their [true] description and the evidence for it," which serves as the answer to Ibrahim, peace be upon him, that is to follow.

The Second: It is the regression from debating him—peace be upon him—with falsehood in their saying: (Who has done this to our gods?) and their saying: (Have you done this?), to debating him with the truth in their saying: (You have surely known...), because this is a negation of power for the idols and an admission of their incapacity and that they are unfit for divinity. It is called naks (overturning), even though it is the truth, because it did not yield for them a firm conviction; rather, it is an "overturning" relative to the falsehood they were upon, in that they admitted to their incapacity while still persisting in their disbelief. In the commentary, there is a similar approach, but it assesses the regression as being from the debate regarding him in their saying: (Indeed, you are the wrongdoers), to the debate with him—peace be upon him—using falsehood in their saying: (You have surely known...).

The Third: That naks is a hyperbole for their bowing of their heads out of shame, and their saying: (You have surely known...), etc., is a projection of bewilderment. For this reason, they presented what is actually an argument against themselves. It is permissible that it be a metonymy for extreme bewilderment and the collapse of their argument, for this does not contradict the literal meaning. The author of al-Kashf said: "This is a good interpretation, as is the first."

The interpretation that the intent is an "overturning in opinion" was narrated by Abu Hatim from Ibn Zayd, and it applies to the first two aspects. Mujahid said: The meaning of (They were overturned upon their heads) is that the followers were turned back upon the leaders; thus, by "heads" (ru’us), the leaders (ru’asa’) are meant.

To me, the third aspect is the most apparent. Regardless of which interpretation is taken, the prepositional phrase (‘ala ru’usihim) is linked to nukisu. It is also permissible for it to be linked to an elided term that functions as a state (hal), and the oath-containing sentence is the object of an implied speech—that is, "saying: (You have surely known)..." etc. The address in (You have known) is to Ibrahim, peace be upon him, not to anyone capable of being addressed. The negated sentence occupies the position of two objects if ‘alima (to know) is transitive to two, or the position of one object if it is transitive to one. The intent is the continuity of the negation, not the negation of continuity, as the present tense form might suggest.

Abu Haywah, Ibn Abi ‘Ablah, Ibn Miqsam, Ibn al-Jarud, and al-Bakrawi (both from Hisham) read it with a shaddah on the kaf (nakkasu). Ridwan ibn ‘Abd al-Ma’bud read nakasu with a light kaf, in the active voice—meaning: they overturned themselves. It is also said: They were turned back upon their leaders, based on what Mujahid’s interpretation requires.