It also shows that the worship of someone who remains outside the mosque cannot be validly linked to that of the imam inside, even if the person could in theory follow him. For example, if a man were in a house next to the mosque, could hear the imam’s takbīrs, and said to his son, “Let us pray behind the imam while staying here in our house,” such a prayer would not be sound, because attendance at the very place where the congregation is being held is indispensable.

The sole exception is when the mosque is full and people extend into the streets: in that case those outside are counted as part of the congregation so long as the rows remain physically continuous. Without that continuity, anyone outside the mosque cannot validly join the worshippers inside; he must come in person, even if he hears every takbīr.

Someone might ask, “What if a person is ill, unable to come, yet hears the call through the loudspeaker and follows the imam from home?” We reply: he is not to pray behind the imam in that condition; he is excused from attending the congregation. If he was in the habit of praying with the congregation when healthy, the full reward will still be written for him, because the Prophet ﷺ said, “Whoever falls ill or travels will have recorded for him whatever he used to do while he was healthy and resident.” Allah knows best.

1069 – Ibn Masʿūd (may Allah be pleased with him) said, “Whoever would like to meet Allah tomorrow as a Muslim should be constant in these prayers wherever their call is given, for Allah prescribed them for your Prophet ﷺ …”