What does the one praying do if he forgets and stands for the third rak'ah in the tarawih prayer?

Question:
This questioner says: A man entered the mosque while the imam was praying tarawih, and he joined him in the prayer. However, the imam did not sit for the tashahhud and connected four rak'ahs continuously. After the imam's taslim, he prostrated two rak'ahs for the first tashahhud. Is my action correct? Yes. He says: A man entered the mosque while the imam was praying tarawih, and he joined him in the prayer. But the imam, O Shaykh, did not sit for the tashahhud and connected four rak'ahs continuously. After the taslim, the imam prostrated two rak'ahs for the first tashahhud. He asks: Is this action of mine correct?

Answer:
This is not the first tashahhud; this tashahhud and taslim are for the first two rak'ahs. What is it for? What is it for? But it is permissible to pray four rak'ahs with one taslim; this is during the day. As for the night, the Prophet (peace and blessings be upon him) said: If he remembers before he relies on it, he must return, sit for the tashahhud and taslim. And if he has started the recitation, he completes four and prostrates for forgetfulness, as I mentioned?