I joined the imam in the final tashahhud and heard the congregation calling for the next prayer, so I changed my prayer to a voluntary one and prayed with them?

Question:
He says: Honorable Shaykh, may Allah grant you success. He says: I joined the imam for the obligatory prayer in the final tashahhud. When he finished and I stood up to pray what I had missed, I heard the congregation calling for the next prayer. So I changed this obligatory prayer to a voluntary one. And when I finished the voluntary prayer, I joined the new congregation to attain the virtue of congregational prayer. Is this correct?

Answer:
You did well in this; this is good. It is permissible for a person to change an obligatory prayer to a voluntary one in such a case, and to pray with the congregation. Good, this is fine. Yes.