Q: The Imaam lead the Asr Salaah. He broke his wudhu after making 3 rakaats. Another imaam continued the salaah, but he read 2 more rakaats. After the salaah, musallis pointed out this error. The first Imaam then re-started the salaah, but, told the late commers that they can’t join this jamaat and they must make their own jamaat at the back of the Musjid. Why was this the case when the whole Asr salaah was being repeated?
A: The reason the imam told latecomers to read their namaaz (salaah) separately is that when the second imam took over he sat after one rakaat which in reality is the fourth rakaat. Thus the faraaidh of the namaaz was complete. Once the imam stood up for the fifth rakaat then whichever masbooq (one who missed any number of rakaats) followed the imam his salaah is null and void. (SHAAMI V 1 P 599) Thus for ALL latecomers it becomes fardh to repeat the salaah whereas for all the other musallis it is waajib to repeat the namaaz. And the rule is that a person reading fardh cannot be a muqtadee (follower) of a person reading a Waajib.
If the imam did not sit in the fourth rakaat then all five rakaats are null and void. In this case it is fardh for everyone to repeat their salaah and all could partner in one jamaat.