question #1 Sahih al-Bukhari 715, Book 10, Hadith 110 : What should be done if a mistake is made during the prayer?

The Prophet (ﷺ) prayed two rak`at of Zuhr prayer (instead of four) and he was told that he had prayed two
rak`at only. Then he prayed two more rak`at and finished them with the Taslim followed by two
prostrations.