Dr. Mustafa Khattab, the Clear Quran - Surah An-Nisa, ayah 156

Translation of Surah An-Nisa, ayah 156 (4:156)

وَبِكُفۡرِهِمۡ وَقَوۡلِهِمۡ عَلَىٰ مَرۡيَمَ بُهۡتَٰنًا عَظِيمٗا ١٥٦
and for their denial and outrageous accusation against Mary,1

Foot notes

297008

i.e., they slandered Mary by claiming that she conceived Jesus through an illegal relationship.