وَٱلَّيْلِ إِذَا يَسْرِ
Sentence structure
وَٱلَّيْلِ continues the oath. إِذَا introduces a time clause, and يَسْرِ is an imperfect verb with understood subject هُوَ, referring grammatically to the night.
Ayah summary
And He swears by the night as it passes.
وَٱلَّيْلِ — And the night
Grammar: وَ coordinates and is an oath preposition; ٱل defines the masculine genitive noun لَّيْلِ. An omitted circumstantial element is associated with «ٱلَّيْلِ».
إِذَا — when
Grammar: A non-governing time/condition adverb introducing the following verbal clause. This phrase is linked through an omitted element.
يَسْرِ — it passes
Grammar: A third-person masculine-singular imperfect verb with understood subject هُوَ; its final yā is omitted in pause/verse ending.