Tafsir of Al-Hijr 15:90

(Just as We sent down upon the dividers)

It is said: It relates to His saying, the Exalted, "(And We have certainly given you...)" etc., such that it is in the position of an accusative as an adjective for a deleted verbal noun from "We gave you"—meaning: We gave you seven of the often-repeated [verses], a giving just as We sent down [upon others]. This is the meaning of "We sent down upon you that [which We sent down] as a sending down like Our sending down upon the People of the Book."