Surah Al-Baqarah (The Cow), Verse 76

وَاِذَا لَقُوا الَّذِیْنَ اٰمَنُوْا قَالُوْۤا اٰمَنَّا وَاِذَا خَلَا بَعْضُهُمْ اِلٰی بَعْضٍ قَالُوْۤا اَتُحَدِّثُوْنَهُمْ بِمَا فَتَحَ اللّٰهُ عَلَیْكُمْ لِیُحَآجُّوْكُمْ بِهٖ عِنْدَ رَبِّكُمْ اَفَلَا تَعْقِلُوْنَ ۟

Wa izaa laqul lazeena aamanoo qaalooo aamannaa wa izaakhalaa ba'duhum ilaa ba'din qaalooo atuhaddisoonahum bimaa fatahal laahu 'alaikum liyuhaajjookum bihee 'inda rabbikum; afalaa ta'qiloon

“Behold! when they meet the men of Faith, they say: "We believe": But when they meet each other in private, they say: "Shall you tell them what Allah hath revealed to you, that they may engage you in argument about it before your Lord?"- Do ye not understand (their aim)?”

Quran 2:76 (Yusuf Ali Translation)