A man missed the congregation and found one of the worshippers praying, so he thought he was completing the obligatory prayer and joined him, but then it became clear that he was praying a voluntary prayer. What is the ruling on an obligatory-prayer follower joining a voluntary-prayer leader?

The questioner : I went to the mosque to perform one of the prayers and found that the congregation had finished their prayer. I found a man praying alone, and I thought he was completing the obligatory prayer, so I lined up behind him. After he finished and said the closing salam, I stood up to complete my prayer. After I finished, he told me: “I was only praying a regular voluntary prayer, not the obligatory one.” What is the ruling in this case regarding an obligatory-prayer follower joining a voluntary-prayer leader? And do we count as having prayed in congregation, or not?

The Shaykh : It is permissible for an obligatory-prayer follower to join a voluntary-prayer leader. The evidence for this is that Mu'adh ibn Jabal (may Allah be pleased with him) used to pray the night prayer with the Prophet (peace and blessings be upon him), then return to his people and pray that prayer with them, so it would be a voluntary prayer for him and an obligatory one for them. This occurred during the time of the Prophet (peace and blessings be upon him). Whatever occurred during the time of the Prophet (peace and blessings be upon him) and was approved by Allah the Exalted, or approved by the Prophet (peace and blessings be upon him) after he became aware of it, is permissible and prescribed, provided it is an act of worship. Accordingly, we say that it is permissible for an obligatory-prayer follower to join a voluntary-prayer leader, and there is no blame in it, based on the hadith of Mu'adh ibn Jabal (may Allah be pleased with him). Some scholars said: It is not permissible for an obligatory-prayer follower to join a voluntary-prayer leader, because the follower's prayer would be more complete than the leader's prayer, and the follower should not be more complete than the leader. However, this reasoning is opposed to the explicit text, so it has no standing.
Some people answered the hadith of Mu'adh by saying that the Prophet (peace and blessings be upon him) might not have known about it. This answer is not sound. This is because, even if we assume or concede for the sake of argument that the Prophet (peace and blessings be upon him) did not know about it, Allah the Exalted certainly knew about it without doubt. If it were something Allah the Mighty and Majestic did not approve of, He would not have left them to continue with it. For this reason, if something occurs that is hidden from the Prophet (peace and blessings be upon him) and is something Allah does not approve of, He clarifies it, as in His saying: By this verse, we know that any action that occurs during the time of the Prophet (peace and blessings be upon him) and during the period of revelation, and is not rejected by Allah the Mighty and Majestic, is among the permissible matters.
And when the evidence is established and the opposing counter-argument is negated, it is obligatory to follow the requirement of the evidence, and it is permissible for an obligatory-prayer follower to join a voluntary-prayer leader.
As for whether it counts as a congregation? We say: Yes, your prayer with them counts as a congregation. This is because it is recommended that when a group enters a mosque and has missed the prayer, they should pray in congregation so that they obtain the reward of the congregation. However, the reward of this congregation will not be like the reward of the original, primary congregation, because it is usually smaller and because it is delayed relative to the first one.
And the reason I said: It is recommended that they pray in congregation, is because the Prophet (peace and blessings be upon him) said: And whatever is more numerous is more beloved to Allah. This is a general statement that includes the first, original congregation and the second congregation that was due to the necessity of missing the first congregation.
As for the statement of some scholars: Those who come to the mosque after the congregation has finished do not pray in congregation. This is a statement with no evidence. The report they narrated from Ibn Mas'ud (may Allah be pleased with him) is a specific case that allows for various interpretations and causes, which may be known to us or not. Perhaps Ibn Mas'ud (may Allah be pleased with him) returned and prayed in his home for considerations he took into account at that time, such as his fear that if he prayed and the common people saw him, they would think this was a prescribed prayer, or that he did not want to pray behind that imam, or something similar to these reasons. And what indicates this is that the author of al-Mughni (may Allah have mercy on him) mentioned that among those from whom the recommendation of congregation for those who missed the first congregation is reported is Ibn Mas'ud (may Allah be pleased with him), as is known to those who have looked into it.
Accordingly, the statement that a congregation after a congregation, if the first is missed, is a religious innovation and disliked, or something similar to that, is a statement with no basis. Especially since it is established from the Prophet (peace and blessings be upon him) that a man entered and wanted to pray alone, so the Prophet (peace and blessings be upon him) said: So one of the Companions stood with him. This is evidence that a congregation after a congregation is prescribed due to the command of the Prophet (peace and blessings be upon him) for it.
As for the statement of those who said: In this, there is one who gives charity and one who receives it. We say: The case of those who enter after missing the congregation cannot be compared to that. We say: If the Messenger (peace and blessings be upon him) commanded one who had already prayed in congregation to repeat the congregation with this person for his sake, how much more so for those who did not pray in congregation at all? So the recommendation of congregation for both of them is more appropriate, and there is no blame in saying: Each of you is one who gives charity and one who receives it.
Yes, if the second congregation is customary in the mosque such that it is made a regular habit where these people pray and then others come after them to pray, then this is undoubtedly among the matters that are prohibited. Because it leads to the division of Muslims and negligence regarding the first congregation, and harms occur in it. So one must distinguish between a temporary matter and a permanent, continuous matter. Making another congregation in the mosque a regular habit is undoubtedly prohibited, because it is not from the way of the Companions (may Allah be pleased with them).
As for when a group misses the congregation unintentionally, but due to necessity, then in this case, it is undoubtedly recommended that they pray in congregation, and they should not pray individually. And there is no doubt that if each person enters a congregation in the mosque after the imam has said the closing salam, and they say: We will not pray in congregation, each person will pray alone, there is no doubt that this creates division among Muslims. Their gathering behind an imam and praying together is closer to unity and cohesion than each of them separating from the other.
And this is clear to anyone who reflects on it and considers it. Indeed, it is explicit in the hadiths in what we mentioned of the saying of the Messenger (peace and blessings be upon him): And in what we mentioned of his saying: And success is from Allah.

The questioner : May Allah reward you with good.