Tafsir of Ghafir 40:25

(In his claim that he is a messenger from the Lord of the worlds).

(Then when he came to them with the truth from Us), and conveyed to them the command of Allah Almighty, indifferent to their saying "a sorcerer, a liar," (they said), out of rage, fury, and inability to offer a counter-argument: (Kill the sons of those who have believed with him and keep their women alive), meaning: repeat upon them what you were doing to them initially, so that you may deter them from supporting Moses, peace be upon him. The command for the killing and the sparing of lives occurred twice: the first time was when the priests and astrologers informed Pharaoh of a newborn from the Children of Israel who would strip him of his kingdom; and the second time is this one. The pronoun in (they said) refers to Pharaoh and those with him.

It is said: Qārūn did not issue such a statement, but they were [collectively] overpowered by it.

(And the plot of the disbelievers is nothing but in error), meaning in a state of being lost—as one says "the beast has gone astray" when it is lost. The intended meaning is that it avails nothing. The outcome is for the righteous. The "al" (in "the disbelievers") is either for specific reference—where the noun is used instead of the pronoun to censure them for their disbelief and to signal the reason for the ruling—or it is for the generic category, with those mentioned [previously] being included in it primarily. The sentence is an interjection brought into the midst of what was recounted of their falsehoods, to hasten to declare the invalidity of the thunderous threats they displayed and their utter dissipation.