Sharia is not established by this, and succession was only established in the situation of consensus, where he did not need any of this, so that which is not of its meaning cannot be attached to it. And Allah knows best.

Section: If one who does not know how much he has prayed is appointed as a successor, it is possible that he should build upon certainty; if he hits upon the truth, [well and good], otherwise they [the congregation] shall glorify Allah (say "Subhanallah") for him, he returns to them, and he performs the prostrations of forgetfulness (sujud al-sahw). Al-Nakha'i said: He observes what those behind him do. Al-Shafi'i said: He acts, and if they glorify Allah for him, he sits, and he knows that it is the fourth [rak'ah]. Al-Awza'i said: He prays one rak'ah with them, because he is certain of the remaining of one rak'ah, then he steps back and puts forward a man who prays the remainder of their prayer with them, and when he gives the taslim, the man stands and completes his prayer. Malik said: He prays for himself a [second] prayer, and when they finish their prayer, they sit and wait for him. The first three opinions are similar. As for us, regarding his not being appointed as a successor, [it is because] he doubted the number of rak'ahs, so succession was not permissible for him for that reason, like one who is not a successor. As for us, regarding his building upon certainty, [it is because] he is one who doubted and has no [predominant] assumption, so building upon certainty is mandatory, like all other worshippers.

Section: Whoever permits succession has permitted the transfer of a congregation to another congregation for a valid excuse. Evidence for this is that the Prophet (peace and blessings of Allah be upon him) came while Abu Bakr was in prayer; Abu Bakr stepped back, and the Prophet (peace and blessings of Allah be upon him) moved forward and completed the prayer with them. He did this on another occasion; he came until he sat by the side of Abu Bakr on his left, while Abu Bakr was on his right, standing, following the Prophet (peace and blessings of Allah be upon him), and the people were following Abu Bakr. Both hadiths are authentic [agreed upon]. This reinforces the permissibility of succession and transferring from one congregation to another in the event of an excuse. From this, it is derived that if two people perform part of the prayer with an Imam, and when the Imam gives the taslim, one of them follows the other, and the other intends his leadership, it is valid; because it is in the meaning of succession, and whoever did not permit succession did not permit this. If the Imam of the neighborhood is absent from the prayer due to travel, illness, or an excuse, and someone else leads the prayer, and the Imam of the neighborhood arrives during the prayer, and the Imam [who was leading] steps back and the Imam of the neighborhood moves forward and builds upon the prayer of his successor, as the Prophet (peace and blessings of Allah be upon him) and Abu Bakr did, there are two views regarding this: First, it is permissible, because the Prophet (peace and blessings of Allah be upon him) did it, so it is permissible for others to do as he did. Second, it is not permissible, because it is possible that this was exclusive to the Prophet (peace and blessings of Allah be upon him), due to the lack of others' equality with him in virtue.

Section: If an invalidator is found in the follower but not the Imam, such as if the follower is in a state of ritual impurity or has impurity on him and did not know of it until after finishing the prayer, or if impurity occurred to him during the prayer, or he laughed [or spoke], or he omitted a pillar, or other such invalidators, and there was no one with the Imam with whom the prayer could be established other than him, the analogy of the school is that his ruling is the same as the ruling of the Imam with him regarding what we have detailed; because the connection of the Imam's prayer with the follower is like the connection of the follower's prayer with the Imam. Thus, what was invalidated there is invalidated here, and what was valid there is valid here. And Allah knows best.

Section: Ahmad, may Allah have mercy on him, said regarding two men, one of whom led the other in prayer, and each of them smelled a scent or heard a sound and believed it was from his companion, and each says it was not from me: They both perform ablution and pray [again]; their prayer was invalidated only because each of them believes...