The ruling on one who stands for an extra rak'ah out of ignorance after the imam forgets the first tashahhud

Question:
The issue is that the honorable imam led our mosque in the 'Asr prayer and forgot to sit for the first tashahhud. After the prayer ended, I stood up to the circle of the rak'ah in which he had forgotten to sit for the first tashahhud, thinking that he had left out a pillar, and that I had to repeat the prayer.

Answer:
No, you did not intentionally add to the prayer. You were ignorant of the ruling, so your ignorance is an excuse. But do not do it a second time. The imam is required to perform the prostration for forgetfulness. When the ma'mumin alerted him that he had left out the first tashahhud, they should have alerted him after the taslim, and he should perform the prostration for forgetfulness. The prostration for forgetfulness is sufficient. Yes, if you had alerted the imam and he performed the prostration for forgetfulness, that would have been enough. But your doing this addition out of ignorance does not invalidate your prayer. Yes.