فَبِأَىِّ ءَالَآءِ رَبِّكُمَا تُكَذِّبَانِ
Fabi ayyi aalaaa'i Rabbikumaa tukazzibaan.
Przeto które z dobrodziejstw waszego Pana uważacie za kłamstwo?
So which of your Lord's blessings will the two of you deny?
Every occurrence of this refrain takes its force from the verse just above it, and here that verse has God at work every single day, which makes the favour in question his continuous attention rather than any one gift. The two being addressed are jinn and humankind, named outright a few verses later; the Arabic is dual throughout, which English cannot show. In recitation the repetition works like a response line, leaving a beat after each item for the hearer to answer.