«فَاسْتَهْوَانَا السَّمَرُ إِلَى أَنْ غَرَبَ الْقَمَرُ وَغَلَبَ السَّهَرُ»
Our night conversation absorbed us until the moon set and wakefulness prevailed.
Samar is evening conversation; sahar is being awake at night. The similarity of sounds adds rhythm, while the setting moon marks time passing.
The scene communicates how fully the companions enjoy their discussion: only late in the night does the passing hour become apparent.