﴿ وَيَقُولُونَ سُبْحَٰنَ رَبِّنَآ إِن كَانَ وَعْدُ رَبِّنَا لَمَفْعُولًۭا ﴾

“and say, "Limitless in His glory is our Sustainer! Verily, our Sustainer's promise has been fulfilled!"”

(Saying: Glory to our Lord!) they exonerate Allah from having a son or partner. (Verily the promise of our Lord) regarding the sending of Muhammad (pbuh) (must be fulfilled) is true and must happen.