I caught up with the imam in the middle tashahhud of Maghrib, and after the taslim I stood for the first rak'ah and did not sit for the sitting, so what is the ruling on my prayer?

Question:
During the Maghrib prayer, I caught up with the imam at the second-to-last sitting, and I completed the last rak'ah with him. Then, after the imam's taslim, I stood to perform the two rak'ahs. I performed the first rak'ah, then stood up without sitting, and performed the second rak'ah. I sat for the final sitting and said the taslim. However, some people said that it is obligatory for you to sit when performing the first rak'ah, then advance, then stand and perform the second rak'ah, sit for the final sitting, and say the taslim. Please inform us of the ruling on what I did and the validity of what they said. May Allah reward you with good.

Answer:
What you did is a mistake; you left out the first tashahhud. What they told you is the correct view. It was obligatory for you to stand and perform a rak'ah to add to the rak'ah you caught up with the imam, so that they would be the first two rak'ahs of the Maghrib prayer for you. Then you sit after them and perform the first tashahhud, then stand for the third and final rak'ah, then sit after it for the final tashahhud. This was what was obligatory for you. However, you did this out of ignorance, so your prayer is valid, if Allah wills. But you must know this ruling in the future. Yes.