Musannaf Ibn Abi Shayba 3:2071

Abu Bakr narrated to us, he said: Sufyan ibn ‘Uyaynah narrated to us, from al-Zuhri, from al-A’raj, from Ibn Buhaynah, that the Prophet (peace and blessings of Allah be upon him) prayed a prayer and thought it was ‘Asr. When he was in the third [rak'ah], he stood up before sitting. When he was about to perform the taslim, he prostrated two prostrations.