The Prophet (ﷺ) said: Anyone who is in doubt in his prayer should make two prostrations after giving the salutation.
Sunan Abi Dawud Book 2, Hadith 644
← Previous Hadith This traditions has also been narrated by Muhammad b. Muslim al-Zuhr through a different chain of transmitters and to the same effect. This version adds; He should perform two prostrations before giving the salutation.

Sunan Abi Dawud Book 2, Hadith 643 Next Hadith → The Messenger of Allah (ﷺ) led us in prayer praying two rak'ahs. When he stood up and did not sit (at the end of two rak'ahs) the people stood up along with him. When he finished the prayer and we expect him to give the salutation, he said: "Allah is most great." While sitting and made two prostrations before giving the salutation. Then he gave it.

Sunan Abi Dawud Book 2, Hadith 645