Surah 63:1
"When the hypocrites come to you, they say, ‘We bear witness that you are indeed the messenger of God.’ God knows that you are indeed His messenger, and God bears witness: ‘Surely the hypocrites are liars indeed!’"
The “hypocrites” – after whom this sūra is named – once “believed” but lost faith. By all appearances, and by their words, they are authentic Muslims. However, according to this sūra, their words are false, and they lead many astray. Their behavior is beyond the pale, and Allah will never forgive them.
- from The Quran with Christian Commentary: A Guide to Understanding the Scripture of Islam