Should a traveler, upon entering a mosque and finding a congregation other than the original mosque congregation, pray with them and complete his prayer, or pray alone and shorten it? And is it permissible for two congregations to pray simultaneously in one mosque at the same time?

First: The congregational prayer is not waived for a traveler except for an excuse.

Second: Whoever misses the first congregation due to an excuse, and enters the mosque to find a congregation praying, it is permissible for him to join them in prayer.

Third: It is not permissible to establish two congregations in the mosque at the same time if one of them is the regular congregation, or if the mosque is small. However, if a traveler enters the mosque and finds a congregation praying – and they are not the regular congregation – he may join them, or perform another congregational prayer if the mosque is large.