Q118 :I went late into the mosque for Friday prayer.
The congregation had started. I joined them, but I soon realized they
had already finished the major part of the prayer. When I stand up for
completing my prayer, how many rak'ahs should I offer?
A118 : When you join a congregation which has
already started, a rak'ah is counted complete for you if you join
before the imam stands up after bowing i.e. rukoo'. If you join
immediately after rukoo', then that rak'ah is not counted for you. It
is preferable, however, to join it even with the parts which will not
be counted. For joining Friday prayer with the imam, you must at least
catch up with one full rak'ah of it. In other words, you must join
before the imam has raised his head after rukoo' of the second rak'ah.
If you join him after that, i.e. having missed both rak'ahs with him,
then you offer four rak'ahs after he has finished. These four rak'ahs
are counted as Dhuhr prayer, which becomes obligatory if you have
missed Friday prayer.
Our Dialogue ( Source : Arab News - Jeddah )