وَهُوَ يَطْبَعُ الْأَسْجَاعَ
And he was stamping out finely shaped passages of rhymed prose.
Yaṭbaʿu literally evokes impressing a stamp or imprint. Asjāʿ is the plural of sajʿ, prose with corresponding sounds at phrase endings.
The passage is describing crafted oratory, not necessarily poetry in a formal meter.