﴿ وَيَقُولُونَ ءَامَنَّا بِٱللَّهِ وَبِٱلرَّسُولِ وَأَطَعْنَا ثُمَّ يَتَوَلَّىٰ فَرِيقٌۭ مِّنْهُم مِّنۢ بَعْدِ ذَٰلِكَ ۚ وَمَآ أُو۟لَٰٓئِكَ بِٱلْمُؤْمِنِينَ ﴾

“For, [many are] they [who] say, “We believe in God and in the Apostle, and we pay heed!” - but then, some of them turn away after this [assertion]: and these are by no means [true] believers.”

Please check ayah 24:52 for complete tafsir.