Tafseer Ibn Kathir of AL KAHFI [20]

إِنَّهُمْ إِن يَظْهَرُوا عَلَيْكُمْ يَرْجُمُوكُمْ أَوْ يُعِيدُوكُمْ فِي مِلَّتِهِمْ وَلَن تُفْلِحُوا إِذًا أَبَدًا

Indeed, if they come to know of you, they will stone you or return you to their religion. And never would you succeed, then - ever."