فَبِأَىِّ ءَالَآءِ رَبِّكُمَا تُكَذِّبَانِ
Fabi ayyi aalaaa'i Rabbikumaa tukazzibaan
تو تم اپنے پروردگار کی کون کون سی نعمت کو جھٹلاؤ گے؟
So which of your Lord's blessings will the two of you deny?
Tukadhdhiban is takdhib, pronouncing a thing false, which is a heavier charge than disbelief, since it assumes the item has already been set out and looked at. Bi-ayyi then asks which one, singular, pushing the hearer to name a particular favour rather than wave the whole set away. Here the item set out is a boundary keeping two waters from swallowing each other.