Tafsir of Al-Hijr 15:66

(And We decreed to him that matter): meaning, We revealed to him that matter, having decreed and established it. The verb qaḍaynā (We decreed) incorporates the meaning of awḥaynā (We revealed); thus, it takes the same transitive construction [as the latter]. Treating the incorporated meaning as a state (ḥāl)—as we have indicated—is one of the two famous views regarding inclusion (taḍmīn).

"That" (dhālika) is indefinite, explained by [the phrase] (that the root of these [people] would be cut off), acting as an appositive (badal) to it, as al-Akhfash stated. Abu al-Baqa’ permitted it to be an appositive to "the matter" (al-amr), if it is taken as an elucidation of "that," rather than as a separate entity. Al-Farra’ held that "that" (dhāka) implies the omission of the preposition bā’—meaning, bi-anna dābira (that the root, etc.). Perhaps what is alluded to by "that matter" is the command contained in the words of the Exalted: "And proceed wherever you are commanded." The bā’ is for accompaniment (mulābasah), and the prepositional phrase is in the position of a state; meaning: We revealed that matter concerning his salvation and the salvation of his household, accompanied by the elucidation of the state of his criminal people, namely, that their root would be cut off. This is excellent, though it is not free from some difficulty.

Zayd ibn Ali and al-A’mash (may Allah have mercy on them) recited it as inna (with a kasrah on the alif). This is explained as an explanatory initiation (isti’nāf bayānī), as if it were asked: "What is that matter?" and it was said in reply: "Indeed, the root, etc." Or it may be an appositive, based on the principle that revelation (waḥy) contains the meaning of speech (qawl). It is said that this is supported by the reading of ‘Abdullah [ibn Mas’ud]: "And We said: Indeed, the root, etc." However, this is an interpretive reading, not [canonical] Quran, as it contradicts the script of the Mushaf.

"The root" (ad-dābir) is the last part. The intent is not merely the cutting off of their end, but their total eradication, such that not one of them remains.

(In the morning): meaning, entering into the morning; for [the verb form] af’ala denotes entering into a state, such as athama (to enter the Tihamah) and anjada (to enter the Najd). It is derived from aṣbaḥa (to become morning) in its complete sense. It is a state (ḥāl) of "these people." This is permissible on the basis that the possessor of the state is part of the possessive construction, and it has been said: It is permitted for the state to proceed from the genitive noun (muḍāf ilayh) when the possessive noun (muḍāf) is such [a part]. The operative factor is not the meaning of possession, contrary to the view of some. To consider it as [describing] the demonstrative pronoun is an error, for no one has said that the possessor of the state operates upon the state itself.

Abu Hayyan chose the view that it is a state of the hidden pronoun in "cut off" (maqṭū’) which refers back to "the root" (dābir). This is permissible despite the difference in number (singular vs. plural) in consideration of the meaning, for "the root of these" has the meaning of "the roots of these," so the state and its possessor agree in [the plural] sense. Al-Farra’ and Abu ‘Ubayd estimated [the syntax as]: "when they are in the morning," as one says, "You, while riding, are better than you while walking." This is critiqued by stating that if it is an estimation of meaning, it is correct; but if it is an explanation of syntax, there is no necessity for it, as is not hidden.