Nasai

851. Commentary: This narration is also an evidence for those who consider congregational prayer (jama‘ah) to be obligatory (fard), otherwise the Prophet (sallallahu alayhi wa sallam) would have granted the helpless blind Companion a concession. Initially, you (sallallahu alayhi wa sallam) had granted him a concession, but then it became known that he did not live far from the mosque, and the call to prayer (adhan) could be heard there; from such a close distance, he could also come alone. In any case, at the time of congregation, there are many who come from such distances, and someone or the other will bring him along. It seems that initially you (sallallahu alayhi wa sallam) thought that this man lived far away, had no companion, and would not be able to come alone. This is not a change in ijtihad (independent reasoning), nor is it necessary for any new revelation (wahy) to descend for this; rather, this fatwa depends on the circumstances of the questioner. Some scholars have said that the command to attend is for recommendation (istihbab), not obligation (wujub), but in light of the above explanation, this view is not strong.