Tafsir of Al-Adiyat 100:11

(Indeed, their Lord): That is, those who are resurrected. He alluded to them after the second revival with the pronoun used for rational beings, after having referred to them previously with what He did, based on their disparity in the two states.

(Concerning them): That is, concerning their essences, their attributes, and their conditions in all their details.

(On that day): That is, the day on which occurs what has been enumerated of the resurrection of what is in the graves and the bringing forth of what is in the breasts. Both adverbial phrases relate to His saying, Exalted is He, (is [fully] acquainted): That is, knowing the outward aspects of what they did and the inward aspects thereof—a knowledge necessitating recompense and connected to it, as indicated by its restriction to that day; otherwise, His absolute knowledge, Mighty and Majestic is He, encompasses what has been and what will be.

Abu al-Summal and al-Hajjaj read: Anna rabbahum bihim yawma'idhin khabir (that their Lord, concerning them, on that day, is acquainted), with the hamza of anna opened and the omission of the emphatic lam. In this case, anna and what follows it are interpreted as a verbal noun (masdar) governed by yaʿlam (He knows), according to what some have regarded as most apparent. This has been used to support the view that yaʿlam is blocked from operating on anna rabbahum in the reading of the majority because of the lam. On this view, it is not permissible for it to relate to khabir (acquainted) either, because it is within the connection of the masdariyyah (verbal noun) anna, and its governed element cannot precede it. Its ruling is known from what has preceded.

It is also said that the speech is based on the estimation of a lam of causality, and it relates to ḥuṣṣila (was brought forth), as if it were said: "And what is in the breasts was brought forth, because their Lord, concerning them, on that day, is acquainted." The first interpretation is more apparent, and Allah, Exalted is He, is All-Knowing and All-Informed.