How to Pray for One Who Joins the Imam in the Final Tashahhud of Maghrib

The question: And the first letter of this episode came to us from a guest of Allah, Ibn Abdulaziz al-Mutairi. He says in his letter: If I enter the Maghrib prayer while the congregation is in the final tashahhud, and I enter with them, then the imam says the taslim and I stand up to complete the prayer, do I pray one rak'ah and sit for the first tashahhud, or do I pray two rak'ahs and sit for the first tashahhud and then come to a third? Please inform us, may Allah reward you.
The answer: In the name of Allah, the Most Merciful, the Bestower of Mercy. O Allah, send prayers and peace upon the Messenger of Allah, and upon his family and his Companions.
As for what follows: If a worshipper enters while the imam is in the final rak'ah, in the tashahhud or in the prostration, he enters with him and completes the prayer with him. Then, when the imam says the taslim, he stands up and performs two rak'ahs, then sits for the first tashahhud, and then comes to the third. This is the legislated manner of performing the Maghrib prayer for one who missed the entire prayer. As for one who missed only one rak'ah, after the imam says the taslim, he stands up and performs one rak'ah, which becomes his second, and he sits and performs the first tashahhud and sends prayers upon the Prophet (peace and blessings be upon him), then he stands up for the third to complete his prayer. And success is from Allah.
The presenter: May Allah reward you.