Surah Al-Baqarah, verse 76

وَإِذَا لَقُوا۟ ٱلَّذِينَ ءَامَنُوا۟ قَالُوٓا۟ ءَامَنَّا وَإِذَا خَلَا بَعْضُهُمْ إِلَىٰ بَعْضٍ قَالُوٓا۟ أَتُحَدِّثُونَهُم بِمَا فَتَحَ ٱللَّهُ عَلَيْكُمْ لِيُحَآجُّوكُم بِهِۦ عِندَ رَبِّكُمْ ۚ أَفَلَا تَعْقِلُونَ ﴿٧٦﴾

2:76 And when they meet the believers they say, “We believe.” But when they meet one another in private they say, “Are you telling them what Allah has revealed to you [about Mohammad], so that they may argue against you before your Lord? Have you no sense?”