Musannaf Ibn Abi Shayba 3:300

Yahya ibn Sa'id and Abu Khalid al-Ahmar narrated to us, from Muhammad ibn 'Ajlan, from Muhammad ibn Ibrahim, from 'Amir ibn Sa'd, who said: The Prophet, peace and blessings of Allah be upon him, commanded the placing of the palms and the setting upright of the feet during prostration.