The Ruling on Having Multiple Congregations in One Mosque

Question:
May Allah reward you. Honorable Shaykh, this questioner says: We are young men who entered the mosque of one of the sheikhs while we were traveling, and we missed the first congregation. We found a group praying, and there were only two of them. One of our young men said, "Pray with them; they are praying alone, and we are a congregation." We told him, "These people are a congregation, and it is not permissible for us to establish another congregation." He said, "They do not show the signs of prayer; they are busy." That is what he says. And we are more numerous and better than them. The question is: Is it permissible for us to join them, or should we pray alone?

Answer:
It is permissible to have multiple congregations in one mosque. So if you find a group praying, join them. Join them, and follow the imam. If he completes the prayer, you are required to complete it, even if you were following him.
And if the imam is a traveler and you are residents, join him. When he concludes the prayer, stand up and complete your prayer for yourselves, as the Prophet (peace and blessings be upon him) said: "O people of Makkah, we are a traveling people, so complete your prayer for yourselves." It is permissible for the traveler to pray the shortened prayer of the resident, but it is obligatory for him to pray. It is permissible for the resident to pray the shortened prayer of the traveler. And if the traveler prays, the resident stands up and completes his prayer. As for having this group and that group in one place, that is division. We have been forbidden from division and disagreement, and we have been commanded to gather together. Yes.