Is it permissible for a Muslim who arrives at the mosque late, after the imam has concluded the prayer, to follow another person who has stood up to complete his prayer—that is, a masbuq (one who joins the prayer late)?

The questioner : Is it permissible for a Muslim who arrives at the mosque late, after the imam has concluded the prayer, to follow another person who has stood up to complete his prayer—that is, a masbuq (one who joins the prayer late)? And is there any imam who permits this?

The Shaykh : Yes, there are those who say that following in such a manner is permissible, but we see it as being like a second congregation that is started after the first congregation. Our evidence for this is two matters:
The first matter is that this was not transmitted from the righteous Salaf, just as a second congregation was not transmitted from them.
The other evidence—and it is undoubtedly stronger because it is affirmative—is the hadith of al-Mughirah ibn Shu'bah in the two Sahihs. Its essence is that the Prophet (peace and blessings be upon him) was on a journey, so at Fajr he went out to relieve himself and perform wudu. His companions were waiting for him to lead them in the Fajr prayer. It appears that he was delayed according to their custom, so they thought there was a matter that had delayed him. They appointed 'Abd al-Rahman ibn 'Awf to lead them in prayer. Al-Mughirah was with the Prophet (peace and blessings be upon him) as he prepared the wudu—the water used for wudu—and then poured the water on him. He was wearing leather socks (khuffayn), so al-Mughirah intended to remove them; he (peace and blessings be upon him) said to him: ; meaning that he had put on the leather socks while in a state of wudu.
This was the place they had prepared for prayer while on their journey. Here is a point that must be clarified: it is the attention of the Messenger (peace and blessings be upon him and his family) to the congregational prayer, and to designating a place and considering it a prayer area like a mosque, even while on a journey. They might stay there for a day or less than a day, or they would designate a place and orient it toward the qiblah. So whoever wants to pray there knows the qiblah by defining and enclosing this place with a few stones.
So there, when they waited for him in this mosque—I say this because it may be confusing to some that they are a congregation on a journey, and the hadith mentions that they waited for him in the mosque. What is the mosque? It is the temporary mosque. When the Messenger (peace and blessings be upon him) was delayed from them for the aforementioned reason, 'Abd al-Rahman prayed with them. Then, after the Messenger (peace and blessings be upon him) completed his wudu, he and his companion al-Mughirah headed toward the mosque. He saw the people in prayer, and al-Mughirah intended to alert the imam to the arrival of the true imam, who is the Messenger (peace and blessings be upon him). He (peace and blessings be upon him) gestured to him to let them be. Then he (peace and blessings be upon him) and al-Mughirah followed 'Abd al-Rahman ibn 'Awf. Then 'Abd al-Rahman concluded the prayer, and he (peace and blessings be upon him) stood up to pray what he had missed, which was one rak'ah of the Fajr prayer... After he concluded the prayer, the people turned and saw that the imam had become a ma'mum (one praying behind the imam). The matter was great for them, and he saw that in their faces. So he said to them, reassuring them and approving of their action: .
This contains very great meanings, among them reassuring the Muslim that if he does good, and among them that we should remove emotional matters and replace them with legal matters; that is, the official imam was delayed, and there is no obstacle to appointing someone more deserving to be imam so as not to burden the people. My brother, it is not a defect! He comes and finds that we have preceded him in prayer, and so on! No, the Messenger (peace and blessings be upon him) said to them: .
Also, the opposite is not permissible; if there is a system in a mosque where they are delayed five minutes, ten minutes after the adhan, and someone comes and starts the prayer before the imam and takes the lead, that is also not permissible.
The important thing is that he (peace and blessings be upon him), when he said to them: , they were reassured at that time. The point is that it did not come in this hadith or in others that al-Mughirah ibn Shu'bah followed the Messenger (peace and blessings be upon him) in this rak'ah that had been missed by them.
From this, we say: whoever comes to the mosque, or if two people come and are delayed in the mosque, and they are preceded by one rak'ah or more, each of them prays by himself. This is how the practice has been, and this is sufficient, and praise be to Allah, Lord of the worlds.