Tafsir of Al-Mutaffifeen 83:28

"A spring" (‘aynan) is in the accusative case (nasb) as a form of commendation (madh). Al-Zajjaj said it is an accusative state (hal) derived from "Tasnim." It is said that its status as an accusative state is valid, despite its rigidity, because of its description in the Exalted’s saying: "those near [to Allah] drink from it," or because it is interpreted as a derivative noun, such as "a flowing one" (jariyatan). You know that derivation is not strictly necessary.

The preposition ba (in biha) is either extra—meaning "they drink it"—or carries the meaning of "from" (min), meaning "they drink from it." Alternatively, it is due to the verb "drink" (yashrab) implicitly containing the meaning of "to quench" (yarwi), meaning "they drink, being quenched by it," or "the ones near [to Allah] are quenched by it." It may also be a connector of enjoyment (iltidhad), meaning "they drink, enjoying it," or for mixing (imtizaj), meaning "they drink the sealed nectar mixed with it," or for sufficiency (iktifa), meaning "they drink, being satisfied by it." These are the aspects they have mentioned.

Regarding it being a connector of mixing, there is debate. Ibn Mas'ud, Ibn Abbas, Al-Hasan, and Abu Salih have stated: "Those near [to Allah] drink it pure, while it is mixed for the righteous (al-abrar)." The view of the majority is that the righteous are the "Companions of the Right," and the near ones are the "Forerunners." It is as if their drink was pure Tasnim because they were preoccupied away from the sealed nectar by the love of the Ever-Living, the Sustainer. It is the nectar to which no other nectar can be compared, and the wine which those of refined taste have recommended to one another; yet the truth is that one who wastes his life is lost, and he has neither a share nor a portion of it.

Others have said that the "righteous" and the "near ones" in this chapter have the same meaning, encompassing everyone who is favored in Paradise. As for His, the Exalted’s, saying...