Example in the Quran

وَإِذَا لَقُواْ ٱلَّذِينَ ءَامَنُواْ قَالُوٓاْ ءَامَنَّا وَإِذَا خَلَا بَعۡضُهُمۡ إِلَىٰ بَعۡضٖ قَالُوٓاْ أَتُحَدِّثُونَهُم بِمَا فَتَحَ ٱللَّهُ عَلَيۡكُمۡ لِيُحَآجُّوكُم بِهِۦ عِندَ رَبِّكُمۡۚ أَفَلَا تَعۡقِلُونَ

When they meet the believers they say, “We believe.” But in private they say ˹to each other˺, “Will you disclose to the believers the knowledge Allah has revealed to you, so that they may use it against you before your Lord? Do you not understand?”