Sunan Abi Dawud 152

Al-Mughirah b. Shu’bah said :The Messenger of Allah (ﷺ) lagged behind (in a journey). He then narrated this story saying : Then we came to people. ‘Abd al-Rahman was leading them in the dawn prayer. When he perceived the presence of the Prophet (ﷺ), he intended to retire. The Prophet (ﷺ) asked him to continue and I and the Prophet (ﷺ)offered one rak’ah of prayer behind him. When he had pronounced the salutation, the Prophet(ﷺ) got up and offered the rak’ah which had been finished before, and he made no addition to it. Abu Dawud said: Abu Sa’id al-Khudri, Ibn al-Zubair and Ibn ‘Umar hold the opinion that whoever gets an odd number of the rak’ahs of prayer, he should perform two prostrations on account of forgetfulness