Musnad Abu Ya'la al-Mawsili 111:8

Abu Ya'la informed us, he said: It was read to Bishr, he informed you: Abu Yusuf, from Ibn Abi Layla and al-Hajjaj ibn Artah, from al-Hakam, from Miqsam, from Ibn Abbas: That the Messenger of Allah (may Allah bless him and grant him peace) used to deliver the sermon on Friday standing, then he would sit, then he would stand and deliver the sermon. Ibn Abi Layla added a letter, he said: Then he would sit a light sitting.