Ruling on joining the second congregation with the intention of a voluntary prayer

Question:
While the voluntary prayer is being performed, the congregational prayer is established. Should I leave the voluntary prayer and go to the congregational prayer, or should I complete the voluntary prayer? And if I leave the voluntary prayer, how do I exit it in a manner that earns reward?

Answer:
As long as you have prayed the obligatory prayer, praise be to Allah, that is sufficient for you. If you have started the voluntary prayer, complete it; there is no need to interrupt it to pray with the other congregation. If you pray with them before you start the voluntary prayer, you pray with the new congregation; there is no harm in that. However, they do not need you if you pray with them; there is no harm. But if it is one person, pray with him until... you and he are a congregation, based on the statement of the Prophet (peace and blessings be upon him) when a man entered and the people had already prayed, he said (peace and blessings be upon him): So if it is one person, and he missed the prayer, and you stand and pray with him so that you both are a congregation, that is good.
As for if they are a congregation, you have a choice. If you pray with them, you get the reward. If you are occupied with the voluntary prayer, or you leave, there is no harm. For this reason, the Prophet (peace and blessings be upon him) said to Abu Dharr when it was mentioned that in the last times there would be people who delay the prayer from its time, the Prophet (peace and blessings be upon him) said: Yes.