Al-Baqarah - 2:76

وَإِذَا لَقُواْ الَّذِينَ آمَنُواْ قَالُواْ آمَنَّا وَإِذَا خَلاَ بَعْضُهُمْ إِلَىَ بَعْضٍ قَالُواْ أَتُحَدِّثُونَهُم بِمَا فَتَحَ اللّهُ عَلَيْكُمْ لِيُحَآجُّوكُم بِهِ عِندَ رَبِّكُمْ أَفَلاَ تَعْقِلُونَ
[2:76]
And when they meet those who believe they say: We believe, and when they are alone one with another they say: Do you talk to them of what Allah has disclosed to you that they may contend with you by this before your Lord? Do you not then understand?
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)?
And when they fall in with those who believe, they say: We believe. But when they go apart one with another they say: Prate ye to them of that which Allah hath disclosed to you that they may contend with you before your Lord concerning it? Have ye then no sense?