Distance beyond which one does not have to attend congregational prayer in the mosque
Question

                Asalamu-Alaikum,
   If someone is too far away to hear the Athan must he still attend the
      prayer in congregation?
   Jazak-Allah
Praise be to Allah.If we assume that the muezzin is giving the call to prayer from the
    roof-top of the mosque (without the aid of amplifiers), that he has a good strong voice,
    that the one who hears him has good hearing, that the wind is calm and that there are no
    barriers or noise that will prevent the sound from reaching people, then the person who
    does not hear this call because of being far away is not obliged to attend the
    congregational prayer in the mosque. Imaam Ahmad estimated the distance at which the voice
    of the muezzin would be inaudible in such circumstances as being more than a farsakh (one
    farsakh is approximately five kilometers). And Allaah knows best.