Once Allah's Messenger (ﷺ) led us in prayer, and after finishing the first two rak`at, got up (instead of sitting for at-Tahiyyat) and then carried on with the prayer. When he had finished his prayer, the people were waiting for him to say Taslim, but before saying Tasiim, he said Takbir and prostrated; then he raised his head, and saying Takbir, he prostrated (SAHU) and then raised his head and finished his prayer with Taslim.
Sahih al-Bukhari Book 83, Hadith 48
← Previous Hadith The Prophet (ﷺ) said, "If somebody eats something forgetfully while he is fasting, then he should complete his fast, for Allah has made him eat and drink."

Sahih al-Bukhari Book 83, Hadith 47 Next Hadith → that Allah's Prophet led them in the Zuhr prayer and he offered either more or less rak`at, and it was said to him, "O Allah's Messenger (ﷺ) ! Has the prayer been reduced, or have you forgotten?" He asked, "What is that?" They said, "You have prayed so many rak`at." So he performed with them two more prostrations and said, "These two prostrations are to be performed by the person who does not know whether he has prayed more or less (rak`at) in which case he should seek to follow what is right. And then complete the rest (of the prayer) and perform two extra prostrations."

Sahih al-Bukhari Book 83, Hadith 49