"Indeed, if they come to know of you," meaning: if they discover you, "they will stone you," meaning: they will kill you with stones, "or return you to their religion," meaning: disbelief, "and you will never succeed, then, ever," if you were to do that.
Surat al-Kahf, from (verse 21 to verse 22).
﴿إِنَّهُم إِن يظهروا عَلَيْكُم﴾ أَي: يطلعوا عَلَيْكُم ﴿يرجموكم﴾ يَقْتُلُوكُمْ بِالْحِجَارَةِ ﴿أَوْ يُعِيدُوكُمْ فِي ملتهم﴾ الْكُفْرِ ﴿وَلَنْ تُفْلِحُوا إِذًا أَبَدًا﴾ إِن فَعلْتُمْ.
سُورَة الْكَهْف من (آيَة ٢١ آيَة ٢٢).
