Congregational Salat (prayer) is obligatory.

Narrated Abu Huraira:

Allah's Apostle ﷺ said, "By Him in Whose Hand my soul is I was about to order for collecting fire-wood (fuel) and then order Someone to pronounce the Adhan for the prayer and then order someone to lead the prayer then I would go from behind and burn the houses of men who did not present themselves for the (compulsory congregational) prayer. By Him, in Whose Hands my soul is, if anyone of them had known that he would get a bone covered with good meat or two (small) pieces of meat present in between two ribs, he would have turned up for the 'Isha' prayer.'

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ " وَالَّذِي نَفْسِي بِيَدِهِ لَقَدْ هَمَمْتُ أَنْ آمُرَ بِحَطَبٍ فَيُحْطَبَ، ثُمَّ آمُرَ بِالصَّلاَةِ فَيُؤَذَّنَ لَهَا، ثُمَّ آمُرَ رَجُلاً فَيَؤُمَّ النَّاسَ، ثُمَّ أُخَالِفَ إِلَى رِجَالٍ فَأُحَرِّقَ عَلَيْهِمْ بُيُوتَهُمْ، وَالَّذِي نَفْسِي بِيَدِهِ لَوْ يَعْلَمُ أَحَدُهُمْ أَنَّهُ يَجِدُ عَرْقًا سَمِينًا أَوْ مِرْمَاتَيْنِ حَسَنَتَيْنِ لَشَهِدَ الْعِشَاءَ ".