Which one should I join when there are two simultaneous congregational prayers in the Masjid? The two congregational prayers are in the same Masjid but not in the same hall, as there is a wall separating them. Please advise. Thank you.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

There should be no more than one congregational prayer at a time in the Masjid, as this disunites Muslims and causes confusion. When this takes place unintentionally, as when there are two halls in the Masjid and the second congregational prayer did not know about the first one, you should join the one with the better Imaam, as when one Imaam recites the Quran correctly while the other is uneducated or if his leadership of prayer is controversial because he commits Bid‘ahs (innovations in religion) or acts of disobedience. If they are equal in degree or you do not know who is better, you should join the congregational prayer with a larger number. The Prophet, sallallaahu ‘alayhi wa sallam, said: "A man’s prayer offered with another man is better than his praying on his own, and his praying with two men is better than his praying with one man. The more there are the more beloved it is to Allaah." [Abu Daawood and An-Nasaa’i, with a Hasan chain of narration]