«فَلَمْ يَكُنْ إِلَّا كَلَمْحِ الْبَصَرِ أَوْ هُوَ أَقْرَبُ حَتَّى أَنْشَدَ فَأَغْرَبَ»
Almost in the blink of an eye—or even faster—he recited a remarkably original verse.
Lamḥ al-baṣar is a conventional expression for extreme quickness; aghraba signals an unusual or striking performance.
Speed is part of the narrative test. The stranger does not withdraw to prepare a response. Within the story, spontaneous composition is offered as evidence of deep command of poetic language.