Musannaf Ibn Abi Shayba 3:4054

Yazid ibn Harun narrated to us, from Shu'bah, from Sa'd ibn Ibrahim, from Hafs, from Ibn Buhaynah—(he said: Najibah)—he said: The morning prayer was called, so a man stood up to pray the two rak'ahs. When the Prophet, peace and blessings of Allah be upon him, finished praying, the people gathered around him. The Messenger of Allah, peace and blessings of Allah be upon him, said to the one who prayed the two rak'ahs: "Do you pray the morning prayer as four?"