The Messenger of Allah (ﷺ) offered one of the afternoon prayers with five (rak'ahs), and it was said to him: "Has something been added to the prayer?" He said: 'Why are you asking?' They said: 'You prayed five.' He said: 'I am only human, I forget as you forget, and I remember as you remember.' Then he prostrated twice then ended his prayer.
Sunan an-Nasa'i Book 13, Hadith 81
← Previous Hadith "Alqamah prayed five (rak'ahs) and when he said the taslim, Ibrahim bin Suwaid said : 'O Abu Shibl, you prayed five!' He said: 'Is that true, O odd-eyed one?' Then he prostrated two prostrations of forgetfulness, then he said: 'This is what the Messenger of Allah (ﷺ) did.'"

Sunan an-Nasa'i Book 13, Hadith 80 Next Hadith → Mu'awiyah prayed in front of them, and he stood up during the prayer when he should have sat. The people said tasbih, but he remained standing, then he prostrated twice while he was sitting, after he completed the prayer. Then he sat on the Minbar and said: 'I heard the Messenger of Allah (ﷺ) say: 'Whoever forgets something in his prayer, let him prostrate twice like this.'

Sunan an-Nasa'i Book 13, Hadith 82