مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4329
Musnad of Abdullah bin Mas'ood
It was narrated from `Abdullah that The Messenger of Allah (ﷺ) forgot something in the prayer, then he did the two prostrations of forgetfulness after speaking.
Musnad Ahmad 4358Its isnad is saheeh, Muslim (572)]