Qur'an 9:56

وَيَحْلِفُونَ بِٱللَّهِ إِنَّهُمْ لَمِنكُمْ وَمَا هُم مِّنكُمْ وَلَـٰكِنَّهُمْ قَوْمٌ يَفْرَقُونَ

And they swear by Allah that they are in truth of you, when they are not of you, but they are folk who are afraid.