﴿ فَأَعْقَبَهُمْ نِفَاقًۭا فِى قُلُوبِهِمْ إِلَىٰ يَوْمِ يَلْقَوْنَهُۥ بِمَآ أَخْلَفُوا۟ ٱللَّهَ مَا وَعَدُوهُ وَبِمَا كَانُوا۟ يَكْذِبُونَ ﴾

“whereupon He causes hypocrisy to take root in their hearts, [therein to remain] until the Day on which they shall meet Him" - because they have failed to fulfil the vow which they had made unto God, and because they were wont to lie.”

Please check ayah 9:78 for complete tafsir.