The ruling on one who makes a mistake in the second rak'ah and stands up for the third

Ahmad ibn Muhammad ibn al-Yahya also says in this letter: If the imam makes a mistake in the tarawih prayer and stands up after the second rak'ah, does he go back or does he complete it to the fourth rak'ah?
Answer: He goes back. If he stands up in the tarawih prayer having intended two rak'ahs and then stands up for the third, he should be alerted, and it is obligatory for him to go back, just as if he stood up for the third rak'ah in the Fajr prayer. This is because the Prophet (peace and blessings be upon him) said: Since he intended two rak'ahs, which is the custom in tarawih and is the sunnah, if he stands up for the third, he should be alerted or he should alert himself, and he goes back. Even if this happens during the recitation, or even after the bowing, he goes back, sits down, and recites the tashahhud, completing it along with the salawat upon the Prophet (peace and blessings be upon him) and the supplication. Then he says the taslim, and then stands up for the next taslim, just as if he did this in the Fajr prayer or in the Jumu'ah prayer, he goes back.