فَأْتِيَا فِرْعَوْنَ فَقُولَآ إِنَّا رَسُولُ رَبِّ ٱلْعَٰلَمِينَ
Commentary:
The word رسول here is in the singular while the subject انا and the verbs used are in the dual number. In Arabic it is permissible sometimes to use singular predicate for a subject in the dual or plural number, as they say ھذان رسولی، وکیلی i.e. those two are my messengers and my agents, the words رسول and وکیل being in the singular. The Arabs also say ھؤلاء رسولی i.e. those are my messengers (Bayan). Elsewhere in the Quran (26:78) a similar construction has been used as فانھم عدو لی i.e. they are my enemies, the word عدو being in the singular but giving the sense of a plural.
The word Rasul in the verse is in the singular while the subject inna and the verbs used are in dual. In Arabic, it is permissible sometimes to use the singular predicate for a subject in the dual or plural number (Bayan). See also 26:78.