(22) باب مَا يَفْعَلُ مَنْ سَلَّمَ مِنْ رَكْعَتَيْنِ نَاسِيًا وَتَكَلَّمَ
It was narrated that Abu Hurairah said:
"The Messenger of Allah (ﷺ) led us in praying 'Asr, and he said the salam after two rak'ahs. Dhul-Yadain stood up and said: 'Has the prayer been shortened, O Messenger of Allah (ﷺ) or did you forget?' The Messenger of Allah (ﷺ) said: 'Neither.' He said: 'One of them happened, O Messenger of Allah (ﷺ).' The Messenger of Allah (ﷺ) turned to the people and said: 'Is Dhul-Yadain speaking the truth?' They said: 'Yes.' So the Messenger of Allah (ﷺ) completed what was left of the prayer, then he prostrated twice when he was sitting after the taslim."
Reference: Sunan an-Nasa'i 1226
In-book reference: Book 13, Hadith 48
English translation: Vol. 2, Book 13, Hadith 1227