Among the evidence for the non-prescription of multiple congregations in the mosque is the prescription of the prayer of fear behind a single imam within its time, and the impermissibility of delaying it.

The Shaykh : What confirms the foregoing is that the wisdom of legislation necessitates the non-prescription of a second congregation, because it would eliminate the first. We have found that the Wise Lawgiver did not permit the repetition of the congregation in a time when we cannot imagine any other time when Muslims would be in greater need of the permissibility of repeating the congregation; that is the time of the prayer of fear. The Sunnah mentions many types of the prayer of fear, seven of which are established, or seven of which are authentic, and with the weak hadiths, they reach fifteen types. The important point is that in all these different types of the prayer of the Messenger of Allah (peace and blessings be upon him) for the prayer of fear, there is no second imam. Rather, we find that in all these forms, despite their multiplicity, the Wise Lawgiver maintains the unity of the imam. For example, among the authentic characteristics, it is prescribed that if the enemy is to the north of the Muslims—meaning, if the Muslims face the qiblah, the enemy is behind them, so they cannot turn their backs on the enemy because it would ambush them—the imam divides the Muslims into two groups. One group stands behind him facing the qiblah and prays with him. When this group finishes, the Messenger of Allah (peace be upon him) proceeds to the second rak'ah, while they sit for the tashahhud, say the taslim after one rak'ah, and depart. Then the group that was facing the enemy to the north comes, and they take the place of the first group, exchanging positions, while the Messenger of Allah waits for the second congregation to come and pray behind him.
And as they say in our region in Syria, or in other places, in an inappropriate style: "Yes, what is this hardship, O Messenger of Allah!! What is this confusion? For what purpose? We maintain the status of the imam alone and oblige the people to divide into two groups, but behind a single imam. Two groups out of necessity, but the necessity did not require multiplying the status of the imam here. All these forms we have referred to, and the research would be long if we listed the rest of them; in all of them, we find that the imam is one. Without a doubt, it would have been easier, and much easier, for the Messenger of Allah (peace and blessings be upon him) to pray with one group in two or three rows if it was not feasible, and then he (peace be upon him) would entrust Abu Bakr or another of the Companions. So while he turned toward the enemy, Abu Bakr would turn toward the qiblah to pray with the second congregation. We do not find this even in this critical situation. What is the secret? What is the point? This is very clear: the connection of the congregation to a single imam is an example of unity, cohesion, and solidarity, and this is in a state of need and necessity. So is it conceivable that this Islam, which did not prescribe multiple imams in a state of need and necessity, would prescribe it in a state of safety and tranquility, with people in their homelands and in their homes, safe and secure?! Whoever prescribes this multiplicity of imams there will not prescribe, and has never prescribed, this multiplicity in mosques in the houses of Allah, with people safe and at ease.