Whoever Said The Doubt Should Be Ignored When One Is Confused Regarding (Whether He Has Prayed) Two Or Three Rak'ah Sunan Abi Dawud 1027
Translation
Zaid b. Aslam reported on the authority of the chain of Malik
When any one of you is in doubt about his prayer, and he is certain that he has prayed three [rak'ahs], let him stand up and complete a rak'ah with its prostrations, then sit and recite the tashahhud. When he finishes and nothing remains except to say the taslim, let him perform two prostrations while he is sitting, and then say the taslim.
Abu Dawud said: Similarly, this tradition has been narrated by Ibn Wahb from Malik, Hafs b. Maisarah, Dawud b. Qais and Hisham b. Sa'd. But Hisham projected it to Abu Sa'id al-Khudri.