وَإِذا جاءوكُم قالوا آمَنّا وَقَد دَخَلوا بِالكُفرِ وَهُم قَد خَرَجوا بِهِ ۚ وَاللَّهُ أَعلَمُ بِما كانوا يَكتُمونَ

And when they come to you, they say, "We believe." But they have entered with disbelief [in their hearts], and they have certainly left with it. And Allah is most knowing of what they were concealing.