Musnad Abu Ya'la al-Mawsili 42:209

Abu Khaythama narrated to us, Waki' narrated to us, Dawud bin Qays al-Farra' narrated to us, from 'Iyad bin 'Abd Allah bin Abi Sarh, from Abu Sa'id: That the Messenger of Allah (may Allah bless him and grant him peace) delivered a sermon on the day of the 'Eid while upon his riding beast.