The Prophet (ﷺ) led them in prayer and forgot (how many rak'ahs he had prayed), then he prostrated twice, then he said the salam.
Sunan an-Nasa'i Book 13, Hadith 58
← Previous Hadith The Prophet (ﷺ) prostrated after the salam when he was not sure.

Sunan an-Nasa'i Book 13, Hadith 57 Next Hadith → "The Messenger of Allah (ﷺ) said the salam after three rak'ahs of 'Asr, then he entered his house. A man called Al-Khibaq stood up and said: 'Has the prayer been shortened, O Messenger of Allah?' He came out angry, dragging his upper garment and said: 'Is he speaking the truth?' They said: 'Yes.' So he stood and prayed that rak'ah, then he said the salam, then prostrated twice, then he said the salam (again)."

Sunan an-Nasa'i Book 13, Hadith 59