They heard the Prophet say on his pulpit: "People should desist from failing to attend the congregations, otherwise Allah will seal their hearts, and they will be among the negligent." (Using translation from Ibn Mājah 794)
وَعَنِ ابْنِ عُمَرَ أَنَّهُمَا سَمِعَا رَسُولَ اللهِ ﷺ يَقُولُ لَيَنْتَهِيَنَّ أَقْوَامٌ عَنْ وَدْعِهِمُ الْجُمُعَاتِ أَوْ لَيَخْتِمَنَّ اللهُ عَلَى قُلُوبِهِمْ ثُمَّ لَيُكْتَبُنَّ مِنَ الغَافِلِينَ