وَأَنَّهُ أَهْلَكَ عَادًا الْأُولَىٰ
“And that He destroyed the first [people of] 'Ad”
This ayah is part of Surah al-Najm, which the Prophet ﷺ recited in full at this event -- building to the prostration verse (53:62) that moved even the Quraysh to fall into sajdah with the Muslims.