Musnad Ahmad 31:517

'Abd al-Razzaq narrated to us, Dawud ibn Qays informed us, that he heard 'Iyad ibn 'Abd Allah narrating that he heard Abu Sa'id al-Khudri narrating: "That the Messenger of Allah, may Allah bless him and grant him peace, used to go out on the day of al-Fitr and pray those two rak'ahs."