Musannaf Ibn Abi Shayba 3:2137

Abu Usama narrated to us, he said: Ubaydullah narrated to us, from Nafi’, from Ibn Umar, that the Messenger of Allah (ﷺ) prayed two rak'ahs with the people, then he became forgetful and performed the taslim. A man called Dhu al-Yadayn said to him—and he mentioned the like of the hadith of Ibn 'Awn and Hisham, and their hadith is that he said: "Has the prayer been shortened?" He said: "No." So he prayed two other rak'ahs, then he performed the taslim, then he prostrated two prostrations, then he performed the taslim.