I caught the final tashahhud with the first congregation, so is it permissible for me to change my intention to a voluntary prayer so I can pray with another congregation?

Question:
He says: Honorable Shaykh, may Allah grant you success. I caught the final tashahhud with the congregation, then I heard another congregation calling for prayer, so I changed my intention to a voluntary prayer. I prayed two rak'ahs after the imam’s taslim, then I caught up with them and prayed the obligatory prayer with the second congregation. Is my action correct? And why would one change the obligatory prayer to a voluntary prayer while he is with a congregation? What is the reason for this? There is no reason for it.

Answer:
He should complete his prayer while he is with the congregation, and praise be to Allah, and not change it to a voluntary prayer, because there is no need to change it.