Al-Ma'idah' - 5:61

وَإِذَا جَآؤُوكُمْ قَالُوَاْ آمَنَّا وَقَد دَّخَلُواْ بِالْكُفْرِ وَهُمْ قَدْ خَرَجُواْ بِهِ وَاللّهُ أَعْلَمُ بِمَا كَانُواْ يَكْتُمُونَ
[5:61]
And when they come to you, they say: We believe; and indeed they come in with unbelief and indeed they go forth with it; and Allah knows best what they concealed.
When they come to thee, they say: "We believe": but in fact they enter with a mind against Faith, and they go out with the same but Allah knoweth fully all that they hide.
When they come unto you (Muslims), they say: We believe; but they came in unbelief and they went out in the same; and Allah knoweth best what they were hiding.