Salah with congregation
It is related by Abdullah bin Abbas (R.A.) that the Messenger of Allah (SAW) said: "Whoever hears the call of the Muazzin for prayer with congregation and there is no genuine excuse for him for not responding to it (i.e. of not joining the congregation, and, in spite of it, he prays individually), prayer of his shall not find acceptance with Allah." (Upon it), some Companions (R.A.) said: Messenger of Allah (SAW) what can be a genuine excuse?" "Danger to life or property or sickness," replied the Prophet (SAW). (Abu Dawood and Daarami)