Quran 3:90 from Surah Aal-i-Imraan on Divine Marvels.
إِنَّ ٱلَّذِينَ كَفَرُواْ بَعۡدَ إِيمَٰنِهِمۡ ثُمَّ ٱزۡدَادُواْ كُفۡرٗا لَّن تُقۡبَلَ تَوۡبَتُهُمۡ وَأُوْلَٰٓئِكَ هُمُ ٱلضَّآلُّونَ
English translation: Indeed those who disbelieved after their belief then they increased (in) disbelief never will be accepted their repentance and those they (are) those who have gone astray
Transliteration: inna alladhina kafaru ba'da imanihim thumma iz'dadu kuf'ran lan tuq'bala tawbatuhum wa-ulaika humu al-daluna