Musannaf Ibn Abi Shayba 3:2063

Ibn ‘Ulayyah narrated to us, from Khalid, from Abu Qilabah, from Abu al-Muhallab, from ‘Imran ibn Husayn: That the Prophet, peace and blessings of Allah be upon him, became forgetful, so he prayed one rak’ah, then he performed the taslim, then he prostrated two prostrations, then he performed the taslim.