Tafsir of At-Tariq 86:15

"Indeed, they"—meaning the disbelievers of Mecca—"plot a plot," meaning they devise schemes to invalidate His matter and extinguish His light, or [it means] to invalidate the matter of Allah the Exalted and extinguish the light of the Truth; and the first [interpretation] is more consistent in its arrangement. This [latter] was said to be more beneficial. "A plot," meaning a great one, according to the extent of their capability. The sentence may be an explanatory resumption [isti'naf bayani], as if it were said: "If the state of the Quran is what has been mentioned, then what is the state of those who say about it what they say?" So it was said: "Indeed, they plot a plot."