﴿ إِذْ أَرْسَلْنَآ إِلَيْهِمُ ٱثْنَيْنِ فَكَذَّبُوهُمَا فَعَزَّزْنَا بِثَالِثٍۢ فَقَالُوٓا۟ إِنَّآ إِلَيْكُم مُّرْسَلُونَ ﴾

“Lo! We sent unto them two [apostles], and. they gave the lie to both; and so We strengthened [the two] with a third; and thereupon they said: “Behold, we have been sent unto you [by God]!””

When We sent to them two men and they denied them both from idh arsalnā ilayhim ithnayni fa-kadhdhabūhumā to the end is a substitution for the previous idh ‘when’ so We reinforced them read fa-‘azaznā or fa-‘azzaznā in other words We reinforced the two men with a third and they said ‘We have indeed been sent to you by God’.