Quran 2:76 from Surah Al-Baqara on Divine Marvels.
وَإِذَا لَقُواْ ٱلَّذِينَ ءَامَنُواْ قَالُوٓاْ ءَامَنَّا وَإِذَا خَلَا بَعۡضُهُمۡ إِلَىٰ بَعۡضٖ قَالُوٓاْ أَتُحَدِّثُونَهُم بِمَا فَتَحَ ٱللَّهُ عَلَيۡكُمۡ لِيُحَآجُّوكُم بِهِۦ عِندَ رَبِّكُمۡۚ أَفَلَا تَعۡقِلُونَ
English translation: And when they meet those who believe[d] they say We have believed But when meet in private some of them with some (others) they say Do you tell them what has revealed Allah to you so that they argue with you therewith before your Lord Then do (you) not understand
Transliteration: wa-idha laqu alladhina amanu qalu amanna wa-idha khala ba'duhum ila ba'din qalu atuhaddithunahum bima fataha al-lahu alaykum liyuhajjukum bihi inda rabbikum afala ta'qiluna