Congregational Salat (prayer) is obligatory.

Narrated Abu Huraira:

Allah's Messenger (ﷺ) said, "By Him in Whose Hand my soul is I was about to order for collecting firewood (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.'