Sunan Abu Dawud
1036
Sahih+2

Narrated Al-Mughirah ibn Shu'bah: The Prophet (ﷺ) said: When an imam stands up at the end of two rak'ahs , if he remembers before standing straight up, he should sit down, but if he stands straight up, he must not sit down, but perform the two prostrations of forgetfulness. Abu Dawud said: I have not narrated in this book of mine any hadith from Jabir Al-Ju'fi (one of the narrators) except this one

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid