صَلُّوا بِاللَّيْلِ means “pray during the night.” The following phrase وَالنَّاسُ نِيَامٌ means “while people are asleep.” Here the wāw introduces a circumstantial clause, giving the setting for the prayer. نِيَامٌ means “sleeping people.”
Worship in the quiet of the night can encourage attentiveness and sincerity. Yet this encouragement does not justify neglecting essential sleep, health, the obligatory dawn prayer, or responsibilities toward family. The benefit is sought through balanced, sustainable worship.