A man catches up with the mosque congregation in one or two rak'ahs, and after he has completed the taslim, he finds another congregation, so he stands up to pray with them!!

Question:
May Allah reward you, Honorable Shaykh. This questioner says: A man caught up with the prayer in one or two rak'ahs, then completed the rest after the prayer. After he had completed the taslim, he found another congregation, so he stood up to pray with them. Is his action valid?

Answer:
No, he does not pray with them. It is not out of doubt, but if a person comes and there is no one to pray with him, you pray with him so that he gets the congregation. The Messenger (peace and blessings be upon him) said: If a person comes and there is no one to pray with him, and you have already prayed, it is recommended for you to stand up and pray with him so that you complete the congregation with him. As for if he already has a congregation, he does not need you. Yes.