Musnad Ahmad 482:126

Abu Abd al-Rahman narrated to us, Sa’id—meaning Ibn Abi Ayyub—narrated to us, Yazid ibn Abd al-Aziz al-Ru’ayni and Abu Marhum narrated to me, from Yazid ibn Muhammad al-Qurashi, from Ali ibn Rabah, from Uqbah ibn Amir, that he said: "The Messenger of Allah, peace and blessings of Allah be upon him, commanded me to recite the Mu'awwidhat at the end of every prayer."