Ubaidullah bin Umar Qawariri said," I never missed the evening congregational prayer (prayer with Jamath). But once a guest came to my house and I remained in his company until late. I went out, looking for any mosque in Basra at which I could catch the evening prayer, but to no avail. The people had all prayed and gone home. I returned to my house,saying to myself,'It is reported in tradition that congregational prayer is twenty-seven times more excellent than individual prayer.' So I prayed the evening prayer twenty-seven times over and slept. I saw in a dream that I was with a group of people who were racing on horses, and I was also racing with them on my horse but my horse was falling behind. I kicked my horse to catch up with them but I could not. One of the riders turned to me and said,"Do not urge your horse, for you will not be able to catch up with us." I said,"Why not?" He replied,"We prayed evening in congregation and you prayed it alone!" Therefore, I learned a lesson and was deeply grieved."
Source: The Major Sins Al-Kaba'r By Muhammad bin 'Uthman Adh-Dhahabi, rendered into English by Mohammad Moinuddin Siddiqui.