Musnad Ahmad 31:73

Qutaybah ibn Sa'id narrated to us, Layth narrated to us, from Khalid ibn Yazid, from Sa'id ibn Abi Hilal, from Abu Ya'qub al-Hannat, who said: I witnessed the Fitr (Eid al-Fitr) with Mus'ab ibn al-Zubayr in Medina. He sent for Abu Sa'id and asked him: "How did the Messenger of Allah, may Allah bless him and grant him peace, use to do?" Abu Sa'id informed him: "That the Messenger of Allah, may Allah bless him and grant him peace, used to pray before he would deliver the sermon." So he prayed on that day before the sermon.