Quran 40:84 from Surah Ghafir on Divine Marvels.
فَلَمَّا رَأَوۡاْ بَأۡسَنَا قَالُوٓاْ ءَامَنَّا بِٱللَّهِ وَحۡدَهُۥ وَكَفَرۡنَا بِمَا كُنَّا بِهِۦ مُشۡرِكِينَ
English translation: So when they saw Our punishment they said We believe in Allah Alone and we disbelieve in what we used (to) with Him associate
Transliteration: falamma ra-aw basana qalu amanna bil-lahi wahdahu wakafarna bima kunna bihi mush'rikina