What does one do if he joins the congregation during the final tashahhud?

Question:
The questioner asks about the one who enters the mosque while the imam is in the final tashahhud: does he enter with the imam, or does he pray with a group with him if the imam says the taslim, or do they enter in a group, or do they pray as a group before the imam’s taslim? Please inform us, may Allah reward you.

Answer:
The apparent meaning of the hadith is that they enter with the imam; if they come and he has not yet said the taslim, they enter with him, and if he has said the taslim, they stand up and make up the missed part. This is because he (peace and blessings be upon him) said: , and he did not exclude anything. Therefore, the best and the sunnah (recommended practice) is for them to enter with him, even if he is in the final tashahhud or in the final prostration. However, if they pray as a group by themselves, it suffices and is valid. But what is prescribed for them is to take the general meaning and enter with the imam, based on his saying: .
When the Prophet (peace and blessings be upon him) once lagged behind during the expedition to Tabuk, he missed the Fajr prayer due to a need of his and was delayed past its usual time. The Companions brought forward Abd al-Rahman ibn Awf, and he led them in the Fajr prayer. When the Prophet (peace and blessings be upon him) arrived, he found that they had prayed one rak'ah. So he entered with them, along with al-Mughirah. When Abd al-Rahman said the taslim, the Prophet (peace and blessings be upon him) and al-Mughirah stood up and made up their rak'ah. They did not separate, nor did they delay the imam. Rather, he gestured to him to continue his prayer until he completed it, and he said: . This indicates that if the imam is delayed past his usual time, the mu'adhdhin (the one who calls to prayer) should bring forward someone from among the people of good to lead the people in prayer, and when the imam arrives, he prays with the people.