Fabi ayyi aalaaa'i Rabbikumaa tukazzibaan

فَبِأَىِّ ءَالَآءِ رَبِّكُمَا تُكَذِّبَانِ

Word By Word:

Fabi ayyi: So which

alaa'i: (of the) favours

Rabbikuma: (of) your Lord

tukazzibaan: will ye both deny?

Translation:

Then which of the favors of your Lord will ye deny?

Ayah Tafseer:

And the Ayaah get's repeated to express the importance: Then which of the blessings of your Lord will you both deny.

Source: Yusuf Ali Translations