Chapter Ar Rahman.... Fabiayyi Aalai Rabbikuma Thukazziban
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It will be patently incorrect. The alif is the subject of verb, second person dual.
Salam!
The word تکذبٰن is derived from the root word ک ذ ب, which means "to deny" or "to reject." The addition of the ت (ta) prefix transforms the verb into its passive form, suggesting being denied or rejected.
ف Then
ب with/by
ای only
ءاَلآء this
ربِ Lord of
کُما you both
تُ You are
کَذِٗب being denied/rejected/belied
ان The suffix اٰن (aan) at the end of تُكَذِّبان (tukadhdhibaan) is known as the "حالة عاطفة" (hālatu ʿāṭifah) or the "emphatic mood" in Arabic grammar. This suffix adds a sense of emphasis, intensity, or heightened emotion to the verb. In the specific context of فبای آلاء ربكما تكذبان (fabayi aalaa'i rabbikumaa tukadhdhibaan), the emphatic mood conveys a stronger emphasis on the denial or rejection being discussed. It intensifies the idea that both the parties are vehemently being denied/rejected/belied.However, I am with a view that this suffix اٰن (aan) is added to the prefix تُ in order to make it a dual "you" as in اَلجَمعَان، یخصفان، تذودان، یسجُدان، طآیفتان because such words are always used when there are two nouns present in the ayah.
My Translation Then by only this (ayah/truth) of your Lord you both are being denied?
Peace!